You might be talking about the same thing.

If you are talking about how much time it takes to render an image, that is frame lag. It’s the hard limiting factor of frame rate. A computer can’t display images faster than it can draw them.

If you are talking about time between a change in the world state, and the display showing that change, that is latency. Latency is affected by a few factors including frame rate. A frame rate of 24 adds an average latency of 21ms, and a frame rate of 60 adds an average latency of 8ms. This is because as frames linger for longer, they become increasingly outdated from the actual world state.

When it's low enough, for VR, they're effectively the same problem.