A keystroke is the action of pressing one key on a keyboard — on a computer, a phone, a till, or even an old typewriter. We count them: “That will only take a few keystrokes.” Office workers and computer people use this word all the time; it is ordinary work English, not a playground word and not very formal. One keystroke is one press, not one word, so a long password needs many keystrokes. Though actually, people also stretch it to mean “a tiny bit of typing”: “You are only a few keystrokes away from sending it.” There is a darker use too: keystroke logging is when a program secretly records every key you press. That is still the same meaning — each press is a keystroke — but the purpose is to watch you.