Do not use if you can correctly use a more specific term such as server, operating system, database, or network instead.
back up, backup
Two words as a verb, one word as an adjective or as a noun.
Back up the files before you turn off the computer.
Save the backup copies on a disk.
Usually, a large, fast network that connects other networks.
Do not use in content for a general audience. You do not have to define backbone in content for a technical audience.
One word. Refers to the lighting that makes a flat panel display, such as that on a laptop computer, easier to read.
All right to use as a verb.
Do not use. If you have to explain the procedure, refer to the Shift+Tab key combination.