What is the "abandonment" rule?

I was just playing a blitz game and I blundered into a pawn fork.  I was staring at the position trying to find the best way to minimize the damage.  My clock ran down to about :40 from maybe 2:30.  I was just about to make a move when the game was automatically ended and my opponent was awarded the win "by abandonment".  But I hadn't abandoned the game - I was thinking about my move and I had time on my clock.

Is there some hidden rule that in blitz games you must make a move after so much time?  This is news to me.  I realize I probably wasn't going to win given the time advantage my opponent had, but I also didn't realize I would lose by default just for thinking about my next move.

If that was your 8 move loss, it has to do with the long move timer.

https://support.chess.com/article/338-how-does-game-abandonment-work

Thank you very much for your answer and for providing the link.  I never abandon games - I think that is disrespectful to the opponent, so I am glad to know all of the rules for abandonment.

I was playing a game 10 | 0 and I was waiting for my opponent to move. And then the clock of my opponent was on 6:40. Then it said "Black won by abandonment"

It was unclear because my opponent has more than half of 10 min and because we're at the 14th move .

Can someone please help me?

That would indicate your opponent was disconnected from the live server process for too long and the game was considered abandoned.

His clock was at 7:50 or so and it went to 6:40. It was Black won by abandonment.

Can someone TELL ME THE RULEs PLEASE?

Without knowing the specific game, it's hard to say what may have happened for sure.

https://support.chess.com/article/338-how-does-game-abandonment-work

https://support.chess.com/article/4560-it-says-game-abandoned-but-i-still-had-time-on-my-clock-whats-going-on