— Core Mechanic
A specific thing you can do in or out of combat. Characters typically have 1 action they can perform each turn, along with 1 Bonus Action and 1 Reaction. At level 10 you get 2 actions per turn.
Basic actions are available to all characters, these include: Attack, Dash, Disengage, Dodge, Help, Hide, Ready, Reload, Search, Stabilize, Take Aim, Use Ability, and Use Object.