Here's why:
* It connects two clauses: A clause is a group of words containing a subject and a verb.
* It shows a contrast: "Although" introduces a clause that contrasts with the main clause.
Example:
* Although it was raining, we went for a walk.
In this example:
* "Although it was raining" is a subordinate clause.
* "We went for a walk" is the main clause.
* "Although" shows the contrast between the rain and our decision to walk.