Unique

Unique[] generates a new symbol with a name of the form $nnn.

Unique[x] generates a new symbol with a name of the form x$nnn.

Examples

Generate a unique symbol:

Unique[]
(* $1 *)

With a base name:

Unique[x]
(* x$1 *)

Generate multiple:

Unique[{a, b, c}]
(* {a$1, b$2, c$3} *)

Please visit the official Wolfram Language Reference for more details.