A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should "provide" the feature. Another program that uses them may ensure they are defined by "requiring" the feature. This loads the file of definitions if it hasn't been loaded already.
(Info-goto-node "(elisp)Named Features").
val provide : Symbol.t -> unit(describe-function 'provide)
val require : Symbol.t -> unit(describe-function 'require)
val is_provided : Symbol.t -> bool(describe-function 'featurep)
val all_provided : unit -> Symbol.t list(describe-variable 'features)