A primer is a preparatory or introductory substance, person, or thing. It can refer to a book, pamphlet, or other written material that provides basic information on a particular subject and serves as an introduction to it. In art, a primer is the first layer of paint applied to a surface before additional layers are added.
In addition, "primer" can also be used in various fields such as politics (as a term for a small political party), medicine (to refer to a substance that helps promote the adhesion of two surfaces or materials), and chemistry (a short-chain alcohol used as a reagent).
In summary, "primer" can have different meanings depending on its context but generally refers to something that prepares or initiates an action, process, or substance.