I'm confused! I thought I had won a game and when the message came back it said "game drawn due to stalemate". My opponent had only his king left and on my last move I cornered him with a pawn in front of him and my king at the side. I also had a bishop and a knight but thought my final move  with the pawn would be sufficient for a win as it rendered his king unable to move, thus"checkmate?" Am I wrong? If anyone knows why this has happened please do tell.

If your opponent has no possible legal move to make as you described then it is a draw by stalemate.

It means that as your opponent cannot make a move, you neither won nor lost and nor did your opponent.

It is not enough to leave your opponent with no legal move, you must also have his/her king in check aswell, if it is not in check then it is always a draw

But of course, my good man.

It cannot be checkmate unless your opponent is in check. If your opponent is not in check, but is unable to move, as in this case, the game is declared a draw due to stalemate.

Just one of those rules we all have to live with. 

How does someone rated 1428 not know about Stalemate?

Should have moved Bc3, then the pawn.  That would have got him out of the coroner and then you check him with the pawn.  Now I'll bet you wont make that mistake again.  

How often does it come up?  Why so harsh?

If you're talking about this game, it's a stalemate all right.

It's a stalemate... For checkmate, the King must be in "check" and unable to move out of the way or defend against it.

ADK

It's a tough lesson, but hopefully a valuable one.  You had this at move 60:

60...     Bd2
61. Kb1 a2+
62. Ka1 Bc3#

Thanks for trying to explain but this feels unfair, I trapped him fair and square! He moved in to this position, he could have moved elsewhere and so it was his bad. His king was trapped, not mine and so I still feel this should have been a checkmate victory for me.

I thought that stalemate was when the kings were left going round endlessly and so the game would have no conclusion. Didn't my game clonclude when I rendered his king immobile? If its his move and he can't move then surely that makes me the winner? 

No, it's perfectly fair, and traping an opponent into a stalemate or draw when you're in an otherwise lost positions is one of the most admirable skills in chess so it's hardly "your opponent's bad".  In this case you had a winning continuation, but accidentally threw away the win.  I don't imagine it's a mistake you'll repeat.

 I know you feel like you have been Robbed of a victory, but sorry that is not how the rules work. From your description of the position you outplayed your opponent but it is still a draw due to stalemate.

 I'm afraid it's your bad, he was clever to put his king there hoping you would stalemate him. You need to learn the rules, bad luck but it was your own fault.

from the Laws of Chess:

Article 10: The Completed Game

10.1

The game is won by the player who has checkmated his opponent's king. This immediately ends the game.

10.2

The game is won by the player whose opponent declares he resigns. This immediately ends the game.

10.3

The game is drawn when the king of the player who has the move is not in check, and this player cannot make any legal move. The player's king is then said to be "stalemated". This immediately ends the game.

"Stalemate" is one of those chess terms that has come into people's everyday usage....others are endgame as in "this war has entered the endgame, pawn as in "he's just a pawn in the corporation," checkmate as in "that's checkmate for his plans"  there may be others i have overlooked, but i digress...just trying to add to the conversation.....

My headline got me the answers I needed.Thanks to everyone who replied. I am well aware of the stalemate rule now.Cheers for the support!