The term 'INFINITE ORDINAL NUMBER' refers to a type of number that is used to indicate the position of an element in an infinite sequence. The abbreviation for this term is 'NTH', which is a three-letter word. This type of number is used to describe the order of elements in a set that has no end, such as the natural numbers or the integers. It is also used to describe the order of elements in a set that is not finite, such as the real numbers.