"1 up" in videogames

[Kenji5]

Hello.
I have some questions about some videogames I've played.

When I get 1 life, in the sreen says: "1 up",

Would you please explain:
the function of "up"?
why does it say "1 up"?

Thanks in advance

[Tdol]

Improvement of one, but you haven't reached the maximum. If it's a competitive game you could be one in front.