Virtual IP Address (VIP) is a broad term that usually defines an IP address that does not belong to a specific physical machine or network interface. VIPs are widely used as part of High availability and Fault tolerance solutions for clusters of servers. A common use case for virtual IP addresses is in the creation of Floating IP addresses.
There’s nothing inherently special about a VIP. It is simply an IP address that was available on a given network and that was not statically assigned to any host. The key point is how that IP is managed. It can be used as a Floating IP for failover, or even assigned to all nodes in the cluster at the same time with a ECMP setup.