Seconds are passing constantly, and we never really pay attention to them unless we are timing something, waiting for something, or we happen to be looking directly at a clock. Like most things in the English language, referring to 1/60th of a minute is known as a 'second'. Although, few people are aware that referring to that particular unit of measurement as a 'second' is actually slang.
Let's rewind to the days of Middle English. In the middle ages, people called 1/60 of a minute 'second minutes' because it is the 'second' operation when dividing an hour by sixty. As time progressed, at some point people became extremely lazy and didn't want to say 'second minutes' so they just started saying 'seconds'!