From Longman Dictionary of Contemporary Englishback up phrasal verb1 back somebody/something ↔ upPROVE to say or show that what someone is saying is true Jane would back me up if she were here. There’s no evidence to back up his accusations. These theories have not been backed up by research.2 back somebody/something ↔ up to provide support or help for someone or something The plan’s success depends on how vigorously the UN will back it up with action. The police officers are backed up by extra teams of people at the weekend. → backup3 TDto make a copy of information stored on a computer Make sure you back up.back something ↔ up These devices can back up the whole system.back something ↔ up onto something Back all your files up onto a storage device or Cloud. → backup4 TTC especially American English to make a vehicle move backwards The truck stopped and then backed up.back something ↔ up I backed the car up a little.5 BACK/BACKWARDSto move backwards Back up a bit so that everyone can see. → backup6 if traffic backs up, it forms a long line of vehicles that cannot move The traffic was starting to back up in both directions.7 if a toilet, sink etc backs up, it becomes blocked so that water cannot flow out of it → back→ See Verb table
Examples from the Corpus
back up• The car stopped and then began to back up.• Back up a bit so that everyone can see.• Can you back up a few steps so that I can open the door?• Back the truck up a little more, will you?• Don't forget to back up all the new files you create.• When you write a history essay, you should back up all your points with facts.• I didn't back the document up and lost the whole lot.• Wright was accused of pretending to be injured, and this was backed up by video evidence.• Cindi backed up the car and stopped in front of the door.• They claim they can give us the best deal, but can they back this up with guarantees?From Longman Business Dictionaryback something → up phrasal verb [transitive] COMPUTING to put copies of information held on a computer onto a disk, so that the information is not lost if there is a problem with the computerThis allows users to back up the database without shutting it down. → back→ See Verb table 