Firing and laying off are different things. You're fired if you're more or less at fault (misconduct, not meeting goals, not doing the job requirements, failing a drug test, violating policies, etc, etc); you're laid off if the position is being eliminated.
Sometimes there's a little bit of both; when you eliminate 7000 positions, you may or may not consider recent performance reviews while you're doing it. Sometimes the employer doesn't want to go through the process of firing for cause, so they claim it's a lay-off, etc. But there's a difference.
Layoff is better than the Britishism "made redundant" anyway. The action to make someone's position redundant generally happens at a different time as when the position is declared to be redundant. A merger may make many people's positions redundant, but they won't generally be laid off until a later time when their position is declared redundant.
