Irreversible binomial is a linguistic term coined by Yakov Malkiel in a 1959 article in the linguistics journal, Lingua, and refers to pairs of words on either side of a conjunction such as and that are always used in a particular order.
For example, bread and butter, salt and vinegar, fish and chips, meat and potatoes, gin and tonic, time and tide, cloak and dagger, ladies and gentlemen, knife and fork, and head over heels.
Some such pairs are reversible in parts of the English speaking word - is it cheese and bacon or bacon and cheese, for example? Both versions are used in the UK at least. To some extent is depends on the ratio of cheese to bacon - if you have more cheese than bacon in your sandwich, then you might call it a cheese and bacon sandwich.