A commit is a saved snapshot of selected project changes in Git. It is like writing a dated note in a project journal so you can later see what changed at that point.
After updating a page, a developer can commit those files with a short message describing the change. That snapshot can be compared with other commits or shared with teammates.
A commit normally stays in the local project until it is pushed to a shared place. It records selected changes, not necessarily every unsaved edit on the computer.