Firm which is either currently active on the same relevant market as the company under investigation, or which is able to switch produc- tion to the relevant products and market them in the short term without incurring significant additional costs or risks in response to a small and permanent increase in relative prices (immediate supply- side substitutability).
(See: Commission notice on the definition of the relevant market for the purposes of Community competition law (OJ C 372, 9.12.1997, p. 5).)
Source: Glossary of terms used in EU competition policy, Antitrust and control of concentrations, European Commission, 2002