There are 2 common meanings:
1/Used in military or police force: Reinforcements, support, help.
2/Computer using: create your secured data in case the computer goes down suddenly, mainly to prevent data loss.
1/Police officer shouts via radio: "Shot fired, shot fired. Officer down. Unit 26 to base, we got a situation here. We need back up immediately!" - "Roger, just hold on. Back up are on the way."
2/Before installing Smart Windows Care, we strongly recommend you to back up you data first to prevent yourself from losing important data.