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.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

When a girl or guy breakup the other gets invovled into another relationship right away. Usualy within 2 weeks after the break up. The other person they are invoved with is known as the "backup". Look out for someone they have never introduce you too but yet they always have contact with. They will just say it is only a friend. But the "backup" is the person they go too if your relationship falls through

A dancefloor technique to attract the attention of a partner. Essentially this involes backing your bootie towards your partner and getting close, often thrusting. This technique will initiate a grind type of dancing.

When you drive your car in reverse, you back up.

A bitch move when you don't have the balls for the task at hand. Call for help because you can't bring it to the table.

1. your systems second source of energy if the first ceases to produce
2. what to say when someone is being too forward
3. the thing cars do when they just ran over a curb