A feat represents a talent or an area of expertise that gives a character special capabilities. It embodies training, experience, and abilities beyond what a class provides. See the feats in the Player's Handbook for more information.
At certain levels, your class gives you the Ability Score Improvement feature. Using the optional feats rule, you can forgo taking that feature to take a feat of your choice instead. You can take each feat only once, unless the feat’s description says otherwise.
You must meet any prerequisite specified in a feat to take that feat. If you ever lose a feat’s prerequisite, you can’t use that feat until you regain the prerequisite.