URL: 

1. n. [Production Logging]
The phenomenon in multiphase flow when one phase flows faster than another phase, in other words slips past it. Because of this phenomenon, there is a difference between the holdups and cuts of the phases.
2. n. [Geology]
Relative displacement of two formerly adjacent points that have been separated by faulting. Slip is used to describe motion along a fault with respect to the distance and direction that one side of the fault has moved relative to the other. Slip is a vector, expressed in terms of distance and direction.