Haha I guess I really let my inner nerd show. I'll attempt a brief explanation for anyone who may be interested...
Just a different style of keyboard, a membrane keyboard is the standard, where when you push down a key you get that mushy feel as you are depressing the membrane to create a circuit with the bottom of the board to register the key press. This is really limiting for some people as you can only create 1 circuit at a time which contributing to slower typing. There is also no tactile feedback either which indicates when the key press is registered. This causes many typers to "bottom out" the key which can lead to significant hand fatigue and eventually the dreaded carpel tunnel.
A mechanical board is designed so that each key has its own individual switch on every key. The also click that can be heard and felt (depending on the type of switch you use - blues, browns, blacks etc all offer different benefits).
I originally made the switch to help postpone carpel tunnel as this is a concern of mine, not only since I type all day and make my living by typing but obviously since I am a golfer as well.
Mechanicals will also increase typing speed, it jumped me from mid 80's over 100 wpm within 30 minutes of switching. They keys can simple register more quickly as they are all independent of one another.
Wow dude I thought you were just making all that stuff up and making fun of us nerds in here but you really did wild out nerd style with that one. I had to Google that to read up on it haha