The term 'stand fast' is used as a noun and the meaning that can be figured out of the term is to refuse to abandon your opinion or belief. The following sentence can make you understand the word quite well: Though there was a lot of pressure on Jack but he stood fast on his stand. The above mentioned sentence says that Jack has taken an opinion and even if people put pressure on him he did not change his opinion.

The meaning of the term can be elaborated when the separate meanings of both parts of the term will be elaborated. Stand is a word that is used to convey the idea of being at one place and the word 'fast' though has several meanings, in this context it is used to convey the idea of firmness; as we use the term 'fast colour'.

So the term 'stand fast' can be used to convey the idea of being firm on something.