what is subquery statement in sql

SQl is an Structured Query language. we use some kind of queries to get results from with or without conditions like

SELECT * FROM Tbl_Students WHERE Stu_Marks >70

so this is an simple type of Sql Query statement. sometime we need to use nested query statement known as sub-query statement LIKE

SELECT * FROM Tbl_Student WHERE Stu_Marks > (SELECT Stu_Marks FROM Tbl_Student WHERE Stu_Id = 126 )

so in this query i want to find out those students having marks more than marks of student id no 126.

so these type of queries are known as subquery statement.

Thanks