How do you define corruption?

Transparency International (TI) has chosen a clear and focused definition of the term: Corruption is operationally defined as the abuse of entrusted power for private gain. TI further differentiates between "according to rule" corruption and "against the rule" corruption. Facilitation payments, where a bribe is paid to receive preferential treatment for something that the bribe receiver is required to do by law, constitute the former. The latter, on the other hand, is a bribe paid to obtain services the bribe receiver is prohibited from providing.