What's "back up" mean?

Native speaker’s answer
Rebecca
Here, "back up" means to go back to something in a conversation or return to an earlier point mentioned. It can also mean driving or moving backward, making a spare copy of data, as well as supporting someone. Ex: I backed up my computer this weekend. Ex: Jane backed me up when I talked to the principal. => support and defend Ex: The car's backing up. Move out of the way. Ex: Wait. Go back to what you said just now about penguins!