Actions undertaken by a firm to deter competitors from entering their markets. Such actions could include making large investments of sunk capital, which make it unlikely that rivals could drive it out, or offering long-term low-price contracts to customers. For any given entry decisions by rivals, these policies do not maximize profits, but they may pay because they serve to discourage entry.

• securities market
• securitization
• security
• security of tenure
• segmented market
• seigniorage
• Select Committee on Estimates
• selection
• self-assessment, tax
• self-correcting system
• self-employment
• self-financing
• self-fulfilling expectations
• self-regulation
• sell
• seller's market
• selling costs
• sensitive sectors
• separable utility function
• separation of ownership and control
• sequestration
• serial correlation
• series
• SERPS
• service