The best answer to question "How often should you commit?" would be "More often than you are doing now". Commit every change that you don't think breaks something, But otherwise, the smaller the changes you commit the better.
The word vector comes from the Latin for “carrier”, reason might be the nature of vector to move from one location to another. In physics, a Vector is an object that moves around a physical space. In Data Science and Machine Learning we generalize this idea to think vector as a list of attributes of an object.