1 - What does "M" mean?

2 - Is there ever a time in a cash game where preflop its just you with KK and your opponent that you can fold KK preflop? Today at a cash game this happened. I dont have the actual hand saved but here is basically what happened.

50NL 6max

UTG min raises to $1
Hero raises $3 to $4 (with KK)
Table folds around to UTG
UTG Raises $24 and is all in'

1. M is used in tournaments. It is calculated by adding the Big Blind, Small Blind, and Ante and then dividing your stack by that number. Its an indicator of how large your stack is compared to the blinds/antes.

2. Against a 50BB stack this in an absolute instacall. Im never folding KK unless villain and I both have Over 150 BBs or I have a rediculous read on villain. But at 50BB, I dont care how tight villain is, u absolutely must stack here.