The basic unit of time.
There are 60 seconds in 1 minute and 3,600 seconds in an hour.
In this clock the hand that moves the fastest shows the seconds. It is called the "Second Hand".
One second is approximately the time of one heartbeat when you are resting. You can get a rough count of seconds by saying "One cat-and-dog, Two cat-and-dog, Three cat-and-dog, ... " etc., or you may prefer "a-thousand-and One, a-thousand-and Two, a-thousand-and Three, ... "
Smaller units of time can be used, such as the millisecond (one-thousandth of a second) or microsecond (one-millionth of a second).