Vesting conditions determine whether the entity receives the services that entitle the counterparty to receive cash, other assets or equity instruments of the entity, under a share-based payment arrangement. Vesting conditions are either service conditions or performance conditions. Service conditions require the counterparty to complete a specified period of service. Performance conditions require the counterparty to complete a specified period of service and specified performance targets to be met (such as a specified increase in the entity's profit over a specified period of time). A performance condition might include a market condition.
Vesting conditions are specifically discussed in IFRS 2 Share-based Payment.
Source: Glossary of Terms of IFRSs as at 31 December 2008.