olemus
hulga elementidest koosnev hulk;
ei pea sisaldama selle hulga kõiki elemente,
kuid võib neid sisaldada

Wiktionary:
1. (set theory, of a set S) a set A such that every element of A is also an element of S
The set of integers is a subset of the set of real numbers.
The set {a,b} is a both a subset and a proper subset of {a,b,c}while the set {a,b,c} is a subset of {a,b,c} but not a proper subset of {a,b,c}
2. a group of things or people, all of which are in a specified larger group.
We asked a subset of the population of the town for their opinion.

näide
hulga {1,2} alamhulgad on {} (tühi hulk), {1}, {2} ja {1,2}

ülevaateid
https://en.wikipedia.org/wiki/Subset

https://mathworld.wolfram.com/Subset.html

https://www.mathgoodies.com/lessons/sets/subsets