Frame rate, measured in frames per second (fps), is how many still images play each second to create motion. Higher fps looks smoother but adds more frames — and every frame makes a GIF bigger.
For GIFs, 10–15 fps is the usual sweet spot: smooth enough to look good, low enough to keep the file reasonable. Dropping from 30 fps to 12 fps can cut a GIF's size by more than half with little visible difference.
When you convert a video to GIF you can set the fps to balance smoothness and size.