The word second has several meanings:

1. A unit of time equal to one-sixtieth of a minute. When you count “one Mississippi, two Mississippi,” each count takes about one second. Your heart beats roughly once per second. A microwave might heat your food for 30 seconds. There are 60 seconds in a minute, which means 3,600 seconds in an hour.
2. Coming after first in order or position. The second person to finish a race wins the silver medal. February is the second month of the year. When you take a second helping of dinner, you're going back for more after your first serving.
3. To support or agree with someone's suggestion, especially in a formal meeting. If your friend proposes playing capture the flag at recess and you say “I second that!”, you're showing you agree with the idea. In student council or other organizations, someone often needs to second a motion before the group can vote on it.

The word can also mean something of lower quality, like second-rate work that isn't quite as good as it should be, or seconds at a factory outlet store (items with small flaws sold at lower prices).