olemus
hulga elementidest koosnev hulk, võib sisaldada selle hulga kõiki elemente

Wiktionary:
1. (set theory, of a set S) a set A such that every element of A is also an element of S
2. a group of things or people, all of which are in a specified larger group

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

https://duckduckgo.com/?t=h_&q=subsets&iax=images&ia=images

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

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

https://www.jarad.me/youtube/videos/probability/02_guide_to_subsets/02_guide_to_subsets.pdf