taps (n.)

"a light stroke, as with the fingers; a gentle blow," mid-14c., a noun from tap (v.1) or from Old French tape, from the verb in French.

It is attested from 1680s as "piece of leather or metal plate fastened to the bottom of a shoe or boot in strengthening or repairing it," the sense in tap-dance. Tap (n.) as short for tap-dance is by 1944.

A figurative tap on the shoulder was originally "an arrest" (slang, 1785). The figurative tap on the wrist "mild reprimand" is attested by 1973 (figurative slap on the wrist is from 1900).

I've always been afraid I was going to tap the world on the shoulder for 20 years, and when it finally turned around I was going to forget what I had to say. [Tom Waits, Playboy magazine interview, March, 1988]