SQL subquery is a little tricky to understand. The basic definition is a query within the query you can call it subquery. Yes, this is the correct answer. I have explained how the inner and the main-queries communicate.
Usually, a subquery supplies a list of values based on the main-query. During query execution depends on the inner query outcome, the main-query pulls the data.
Example of Subquery
user_id in (1000, 2000, 3000)
The values in the ‘IN’ list, basically an outcome of the subquery. Here is my post on key ideas to write a subquery
