What does `is_main_query()` return inside a `pre_get_posts` callback?

Question

WordPress Expert — Easy

What does `is_main_query()` return inside a `pre_get_posts` callback?

Accepted Answer

`is_main_query()` returns true if the current query being modified is the main WordPress query, not a secondary custom query. This is useful for targeting specific queries in the `pre_get_posts` hook.