Names

Names["pattern"] gives a list of the names of symbols that match the pattern.

Examples

Find all symbols starting with "Plot":

Names["Plot*"]
(* {"Plot", "Plot3D", "PlotRange", ...} *)

List all user-defined symbols:

Names["Global`*"]
(* {"x", "f", "myVar", ...} *)

Find symbols matching a pattern:

Names["*Q"]
(* {"EvenQ", "OddQ", "IntegerQ", ...} *)

Please visit the official Wolfram Language Reference for more details.