drop dead

Hello, everybody.

I am not sure about "drop dead" although I looked up the dictionary.
Would you help me to understand that?
(It is from a Toronto Sun article.)

On Friday, British lawmakers approved a bill that aims to block a no-deal option that would force Johnson to delay the UK from leaving the EU without a customs agreement. Queen Elizabeth is expected to sign the bill into law Monday.

Johnson, furious about his predicament while leading a minority government, has threatened to call an election for mid-October. But the opposition has rejected his request, not wanting him to dictate its timing.

For now, the drop dead date for the UK to leave – with or without a deal – is Oct. 31. Whether it will be extended for a third time into the new year is anyone’s guess.

Thank you so much.

It is the second definition given below:

WordReference Random House Unabridged Dictionary of American English © 2019
drop-dead (drop′ded′),adj.

1. inspiring awe, astonishment, or envy:a drop-dead guest list; a drop-dead sable coat.
2. being the most extreme limit or possibility: What's the drop-dead date for handing in term papers? That is our drop-dead offer.

In other words, the last possible date/the latest date/the deadline for the UK to leave is October 31.

Language Hound said:

It is the second definition given below:

In other words, the last possible date/the latest date/the deadline for the UK to leave is October 31.

Thank you very much, Language Hound.