main / major / specialize / line of work / field-of-endeavor

This sign means "major (in school), main, field of work, specialize..."

MAIN/major/line of work/field of discipline and other related concepts:
The right flat hand moves forward along the top of the stationary left flat hand.

PROFESSION:
To indicate a "professional," add the "AGENT" sign.

Variation: Some people do this sign using an "index finger" on the dominant hand or even with both fingers in "index finger handshapes.