Perspiration is a polite name for "sweat." Perspiration is what makes you dread gym class and what keeps deodorant manufacturers in business.
Let's face it, sweat is kind of gross — it drips down your face and can even make your body smell badly. But, it doesn't sound so bad if you refer to it as perspiration, does it? Still, perspiration means that salty fluid secreted by your sweat glands, when your body is hot. Perspiration can also be used to mean the process of sweating.