back sb up, to support or help somebody
::: My family backed me up throughout the court case.
back sth up, to prove something is true
::: His claims are backed up by recent research.
backup, (back-up), someone or something that provides, support or help, or something that you have arranged in case your main plans, equiptment etc. go wrong
::: We are going to need some professional backup for this project.
::: The party is going to be outdoors, so we'll need to organize somewhere as a backup in case it rains.
::: Remember, your colleagues are your backup system when things go wrong
put/get sb's back up
::: Just ignore him - he's only trying to put your back up.