遅い (osoi) means "slow" or "late." It's an い-adjective, the opposite of "早い" (hayai). It describes lack of speed (moving slowly) or being behind schedule (late for an appointment). For example, "電車が遅いです。" (Densha ga osoi desu.) means "The train is late."

「遅い」は動きが遅い、または時間が遅れる時に使います。例：電車が遅い。