MAIN CLAUSE & SUBORDINATE CLAUSE

The Main Clause is called as Main Clause or Independent Clause or Principal Clause because it makes complete sense on its own.

To make sense, it is not dependent on any other part of the sentence. 

The Main Clause is like a short sentence within the sentence. 

Let's take an example-

This is the boy who quarrelled with me.

Here, there are two clauses.

This is the boy and who quarrelled with me.

The first clause This is the boy makes complete sense but the second clause who quarrelled with me is not complete. 

So, the first clause is called Main Clause or Principal Clause or Independent Clause. 

Examples:

1. I waited till the bus came.

Main Clause: I waited

2. I know the reason why she took admission in that school.

Main Clause: I know the reason

SUBORDINATE CLAUSE 

The Subordinate Clause known as the Dependent Clause, doesn't make any sense on its own.

It is dependent on the Main Clause to make sense. 

Examples:

1. I waited till the bus came.

Subordinate Clause: till the bus came

2. I know the reason why she took admission in that school.

Subordinate Clause: why she took admission in that school