好胜心 refers to a strong desire to outdo others or to be the best — a competitive drive or ambition. It's a compound noun formed from 好 (hào, 'to like, to be fond of') + 胜 ('to win, to surpass') + 心 ('heart, mind'). The tone of 好 here is hào (fourth tone), not hǎo (third tone), which is a common learner pitfall. This word can be neutral or slightly negative depending on context — in a team setting it might imply a healthy competitive spirit, but in personal relationships it can suggest a stubborn unwillingness to lose.