As a Noun: 1. In mathematics and geometry, the lowest edge or part of a triangle, as in the English expression ‘the base of a triangle’. English = base. Note: 1. Originally only an alternative Australasian Signed English sign for the other Auslan sign for ‘base’. Now this variant is used by some teachers in maths and geometry specifically for ‘base of a triangle’. 2. Apologies for the missing video. The line drawing will be replaced as soon as possible.