A pinch was to squeeze something tightly between two objects, such as one's fingers. One notable tactic which made use of pinching was the Vulcan neck pinch.
Pinching one on the butt was considered a crude romantic overture. (DS9: "Rules of Acquisition", "Fascination")
In 2369, an illusion of Buck Bokai noted that he could pinch himself, causing pain, an argument for his real existence. (DS9: "If Wishes Were Horses")
In 2372, "pinching" was one of the several possible descriptions of back pain The Doctor offered to a pregnant Samantha Wildman, whose unborn baby was putting pressure on her sciatic nerve. She chose "shooting" instead. (VOY: "Tattoo")
In 2377, Doctor Lewis Zimmerman, believing Deanna Troi to be another trick by The Doctor, pinched her arm to see if she real or another hologram. Troi cried out in pain. (VOY: "Life Line")