(1) Short for estimated street price, ESP is a manufacturer or developer's estimated price for a product in a specific region or market sector. The estimated street price is not necessarily the same as the end -user's purchase price.
(2) Short for Encapsulating Security Payload, the ESP header is designed to provide a mix of security services in IPv4 and IPv6. ESP may be applied alone, in combination with the IP Authentication Header (AH), or in a nested fashion. The ESP header is inserted after the IP header and before the upper layer protocol header (transport mode) or before an encapsulated IP header (tunnel mode). ESP is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service, and limited traffic flow confidentiality. [Adapted from (RFC2406)]