IP stands for Intellectual Property and is a generic term used to indicate that the person or entity developing such a property has rights for trademark and copyright protection. In the semiconductor industry an IP typically stands for some kind of a design or implementation idea that someone has developed and is licensing it to others for use. For example, ARM processor cores is an IP as they license it to others for use in their designs.
Similarly a VIP stands for verification IP, and is a property that can be sold to others for use. Because a VIP is intended to be used by many teams, it has to be made configurable to fit the needs of most. A typical example is that of bus agents like AMBA, Wishbone, etc which can be used by multiple teams and configured to fit their needs.
Any design for IP/VIP starts with a requirement, for bus agents the requirement is to meet the protocol. For example a SPI bus VIP agent should cover all scenarios listed in the protocol and have coverage to prove that the agent does handle all corner cases.