I'm a Electrical Engineer (semi retired) and there are many references to the two words mentioned which we now appear to not be able to mention !!!
Two transfomers in a electricity grid station were always reffered to as 'M and S' pretty much anything that has a primary and secondary was always called M and S
The world really has gone mad 
(Now, I must pop out and feed my rainbow sheep with my gender neutral grandchildren) 
Steve