Field of competition law and policy. In the EU context, both the rules governing anti-competitive agreements and practices (cartels and other forms of collusion) based on Article 101 of the EC Treaty and the rules prohibiting abuses of (existing) dominant positions based on Article 102 of the EC Treaty, are commonly referred to as ‘antitrust’.
Source: Glossary of terms used in EU competition policy, Antitrust and control of concentrations, European Commission, 2002
In the US, there term antitrust is used to cover rules governing the above as well as merger control rules.