means The salty fluid your sweat glands release through the skin to cool you down, especially when you're hot, exerting yourself, or nervous.

from From Latin perspirare, 'to breathe through' — per ('through') plus spirare ('to breathe'), the same spirare that gives us respire, inspire, and spirit. The old idea was that the skin quietly breathed, exhaling moisture through its pores. English borrowed the word in the 17th century, and it soon became the polite drawing-room substitute for the blunt, sweaty 'sweat' — hence the genteel old saying that horses sweat, men perspire, and ladies merely glow.