EIP is the acronym for Ethereum-Improvement-Proposal
An Ethereum Improvement Proposal is a technical design document providing information to the Ethereum community, describing new proposed features, processes or environments affecting the greater Ethereum protocol. Suggested changes to the protocol are submitted as a EIP. The author of the EIP is responsible for soliciting feedback and consensus for his or her suggested improvements within the community and documenting dissenting opinions.
EIP & ERC are in essence the same concept. However, EIP are more design oriented specification documents while ERC is the actual digital software implementation of it.