As nouns the difference between multitude and multiple
is that multitude is a great amount or number, often of people while multiple is (mathematics) a number that may be divided by another number with no remainder.
Is multitude singular or plural?
There is confusion over whether nouns of multitude are singular (the collective entity) or plural (the individuals in it). In fact they are both, or rather they can be either. This ambiguity means that there are better and worse ways to use them – but there is no definitive right and wrong way.
What is considered a multitude?
: a great number of things or people. : ordinary or common people as a group.