Let’s talk about the very nice phrasal verb “to back up”.
I love this one because it means to give support or encouragement to other people.
He is is a very good colleague. He backed them up even though he did not agree with their claim.
Note that “to back up” is a separable phrasal verb and therefore we say “backed them up” and NOT “backed up them”
Now, there is a another meaning of “to back up” that I am sure you know.
Look at this example:
Please, remember to back up all important files.
And in this case “to back up” means to make a copy as support usually for security.
“It is always good to have a backup plan.”
And in this quote “backup” written together is an adjective… A “backup plan” is another plan just in case the original one does not work out.