A sprung metal blade on the riser that the arrow slides out from under as you draw. Hit exactly your draw length and it snaps audibly — that click is your cue to release.
The clicker exists because a recurve bow has no mechanical draw stop at all: a compound is limited by its cam system, barebow does without one entirely — only you need an audible signal so every shot gets the same draw length. The most common mistake is fitting it too early: on an unsteady stance with a wandering anchor, the clicker amplifies exactly the uncertainty it is meant to cure. The second is pushing the bow hand forward to reach the click instead of pulling the elbow through with back tension. The coaching line for it: the click comes to you, you don't go to the click. And a warning that rarely gets said out loud — if waiting for the click starts to feel oppressive, tell your coach. Left alone, that hesitation can harden into a blocking pattern — the short road to target panic.