He is learning how to use collective nouns.

In mathematics, an empty set refers to a set that does not contain any elements.

A power set is a set consisting of all subsets of a set.

There is a communal letterbox in our apartment.

This concept is difficult.

He worked hard to accomplish his goals.

His role is the team leader.

In set theory, the symmetric difference indicates the difference between two sets.

She has trypophobia, and feels discomfort when she sees things with many holes like beehives or corals.

Health is very important.