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Antitrust

Glossary of Key Antitrust Terms

Author: Aaron Gott

If you are an executive or general counsel of any business, whether a startup or Fortune 100, you will at some point hire and interact with outside antitrust counsel. This glossary is your guide to dealing with them. It explains essential terms and concepts in U.S. federal antitrust and competition law. Each entry provides a brief, plain-language explanation with corporate legal decisionmakers in mind as the audience with links to more detailed discussions on The Antitrust Attorney Blog and the Bona Law website for readers who want to dive deeper. We focus on U.S. antitrust principles, with a few notes on international standards where relevant. 


Market Structure & Power


Relevant Market

The relevant market defines the boundaries within which competition is evaluated. It includes a product market (substitutable goods) and a geographic market (where competition occurs). Market definition is central to assessing market power and competitive effects in merger and conduct cases.

Further reading from Bona Law:


SSNIP Test

The SSNIP test (Small but Significant and Non-transitory Increase in Price) is a method used to define the relevant market by asking whether a hypothetical monopolist could profitably impose a small (typically 5–10%), lasting price increase. If enough customers would switch to alternatives to make the price increase unprofitable, the market definition must be broadened. This test is central to merger analysis and market definition in both civil investigations and litigation. See also Relevant Market, Monopoly Power.

Further reading from Bona Law:


Market Power

Market power is the ability to raise prices or exclude competitors in a given market. It is often evaluated through market share and competitive conditions. While market power is a prerequisite for several types of antitrust claims, merely possessing it is not illegal.

Further reading from Bona Law:


Monopoly Power

Monopoly power is the ability to control prices or exclude competition. U.S. courts typically require a high market share (often 70% or more) plus other factors like barriers to entry. It is not illegal to possess monopoly power—only to obtain or use it unlawfully.

Further reading from Bona Law:


Concentration / HHI

Market concentration measures how much of a market is controlled by the largest firms. A common tool is the Herfindahl-Hirschman Index (HHI), which is calculated by summing the squares of the market shares of each firm in the market. HHI is often used by the DOJ and FTC to evaluate whether mergers will substantially lessen competition. A higher HHI indicates a more concentrated—and potentially problematic—market. See also HSR Notice, Relevant Market, Market Power.

Further reading from Bona Law:


Monopsony

Monopsony is the buyer-side equivalent of monopoly. It refers to a market in which a single buyer—or a small group of buyers—has significant power to dictate terms to sellers. In antitrust law, monopsony concerns often arise in labor markets (e.g., wages) or agriculture (e.g., poultry processors). While not inherently unlawful, the exercise of monopsony power in a way that harms competition—such as depressing wages or input prices through coordination or exclusionary tactics—can violate the Sherman Act. See also Market Power, Relevant Market, No-Poach Agreement.

Further reading from Bona Law:


Dominance (Dominant Position)

Dominance refers to the EU standard roughly equivalent to U.S. monopoly power, but with a lower threshold. A firm is considered dominant if it can act independently of market pressures. The EU prohibits abuse of a dominant position (not the status itself), with a focus on exclusionary or exploitative conduct.

Further reading from Bona Law:


Conduct


Monopolization

Monopolization occurs when a company acquires or maintains monopoly power through anticompetitive conduct. This is illegal under Section 2 of the Sherman Act. The plaintiff must show both monopoly power and that it was obtained or maintained through means other than legitimate competition. See also Monopoly Power, Market Power.

Further reading from Bona Law:


Cartel

A cartel is a term used to describe an antitrust conspiracy, typically involving per se illegal conduct such as price-fixing, bid-rigging, or market allocation. Cartels are prosecuted both civilly and criminally and are a top enforcement priority for the DOJ and other agencies. See also Price Fixing, Bid Rigging, Market Allocation.

Further reading from Bona Law:


Price Fixing

Price fixing is an agreement among competitors to raise, lower, stabilize, or otherwise control prices. It is a per se violation of the Sherman Act and is frequently prosecuted criminally by the DOJ.

Further reading from Bona Law:


Bid Rigging

Bid rigging is a form of collusion in which competitors conspire to manipulate the outcome of a bidding process. It is often prosecuted as a criminal offense by the DOJ, much like price fixing. It is considered per se illegal.

Further reading from Bona Law:


Market Allocation

Market allocation is an agreement among competitors to divide markets, customers, or territories rather than compete. It is per se illegal and often prosecuted as a criminal violation.

Further reading from Bona Law:


Group Boycott

A group boycott (or concerted refusal to deal) occurs when multiple companies agree not to do business with a particular firm. Some are per se illegal, especially when used to enforce a cartel. See also Cartel, Per Se Antitrust Violation.

Further reading from Bona Law:


Tying

Tying occurs when the sale of one product is conditioned on the purchase of another. It may be illegal if the seller has market power in the tying product. While often treated as per se unlawful, courts sometimes use a more nuanced analysis. See also Exclusive Dealing, Monopoly Power.

Further reading from Bona Law:


Exclusive Dealing

Exclusive dealing requires a customer or supplier to do business only with a specific partner. These arrangements can be lawful or procompetitive, but may violate antitrust law if they foreclose rivals from the market.

Further reading from Bona Law:


Resale Price Maintenance (RPM)

Resale Price Maintenance (RPM) involves a manufacturer setting a minimum price for resellers. While once per se illegal, it is now analyzed under the rule of reason at the federal level. Some states still treat it as automatically unlawful. See also Colgate Policy.

Further reading from Bona Law:


Colgate Policy

Colgate Policy (from United States v. Colgate, 1919) allows a manufacturer to unilaterally announce a minimum resale price and refuse to deal with resellers who do not comply—so long as there is no agreement or coercion. This doctrine provides a narrow exception to resale price maintenance restrictions, but it is easy to cross the line into unlawful coordination. See also Resale Price Maintenance (RPM), Rule of Reason.

Further reading from Bona Law:


No-Poach Agreement

No-poach agreements are deals between employers not to solicit or hire each other's employees. These are generally considered a form of market allocation in the labor market and are often treated as per se illegal. See also Market Allocation, Per Se Antitrust Violation.

Further reading from Bona Law:


Information Exchange

Information exchange among competitors can raise antitrust concerns when it involves competitively sensitive data such as prices, costs, or future business plans. While not per se illegal, information exchanges may violate antitrust law if they facilitate coordination or reduce uncertainty in the market. Trade associations are common settings for these risks. Agencies assess the frequency, age, anonymity, and nature of the data exchanged to determine legality. See also Trade Association, Cartel.

Further reading from Bona Law:


Price Discrimination

Price discrimination under the Robinson-Patman Act, a rarely enforced statute, prohibits certain forms of price discrimination between buyers of commodities. Specifically, it targets situations where a seller offers different prices to competing buyers for the same product, where the effect may be to harm competition. The law contains numerous exceptions and defenses, and its relevance has diminished in modern antitrust enforcement, though Costco's business model has led to a revival of Robinson-Patman Act claims.

Further reading from Bona Law:

Need help with an antitrust issue?

Bona Law represents companies of all sizes — from startups to Fortune 100s — in antitrust counseling, investigations, litigation, mergers, and appellate matters. If any of the concepts in this glossary has come up in your business and you would like to discuss it with experienced antitrust counsel, please contact us.

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