elizabeth_robinson In many cases, "back something" means to support or endorse something. For example, you might say, "I'm backing this candidate for president," meaning that you support or endorse that candidate.
tim_burns Typically, if you "back something," you're supporting it or endorsing it. So if you back a candidate for office, you're saying you support them and their platform.
Sondre_truong Assuming you are asking about the term "back something up", it usually means to support or reinforce something with evidence or logic. For example, if you are trying to prove a point, you would back it up with evidence.
