Pushiness is the way a pushy person behaves: they keep pressing other people until they get what they want. It is a criticism, not a compliment. You might talk about someone's pushiness at work (talking over others, asking again and again, not reading the room) or in a shop or a queue. It is the noun from pushy. English already has better-sounding words for the good side of this — confidence, drive, being proactive — and pushiness is the ugly side: too much force, too little care for other people. It is not a rare word, but people more often just say someone is pushy than name the quality.