定格 originally comes from filmmaking — a freeze frame where the image stops moving. It also refers to the stop-motion animation technique. Figuratively, you can use it to describe a moment fixed in memory or a decision that becomes final (e.g., 定格在脑海中 'frozen in one's mind'). Avoid confusing it with the broader 'to confine to' translation in dictionaries — that sense is rare in modern Chinese.