We always back Tim Bowen 100% when it comes to word grammar.
The word back is most commonly used as a noun or an adverb but it can also function as an adjective and a verb.
As an adjective it has two main meanings. It is used to mean ‘furthest from the front’, as in ‘They made up a bed for him in the back bedroom’ or ‘You’ll find him in the back garden’. It is also used to refer to money that is owed from an earlier date and has not been paid yet, e.g. back pay, back taxes, back rent, as in ‘I’m owed over £700 in back pay’. It can also be used to refer to streets or roads that are away from any main street, as in ‘He usually drives home using the back roads’.
The verb to back has several meanings. The main one is to give support to a person, organization or plan, making them more likely to succeed, as in ‘Both main parties are backing the intervention in Libya’. Used with various adverbial particles or prepositions, it can also mean to move backwards, as in ‘He backed the car slowly out of the garage’ or ‘His opponents have backed him into a corner on this issue’. If you back a horse or a sports team, you bet money that they will win a race or a competition, as in ‘Who are you backing to win the next World Cup? And, in an idiomatic sense, if you back the wrong horse, you support someone or something that fails. If a building or garden backs onto a place, that place is directly behind it, as in ‘Their house backs onto a railway line, so it’s rather noisy’.