The term "mushy" literally means soft or squishy. Normally, when you hit a mushy keyboard, it does not feel crispy Isince it "dampens" the force required to push it, kinda like a bag of cheetos after you left the bag open. Meaning, in order to "push" the keyboard down til the bottom, the required force is much greater, which leaves very little tactile feedback. You can feel this in cheap desktop keyboards. Even if they taste the same, you don't want your cheetos kinda "mushy," don't you?

By the way, "mushy" keyboards don't make you type slower. I can still type my fastest even with crappy rubber domes. Other people don't prefer it because of the "feeling" of it being mushy... which I can totally relate to. If you want to type fast, get a satisfying response, and try to be silent, you can invest in some linear switches (reds, etc) and (optionally) put o-rings to dampen the sound... that is if you are willing to pay the premium. Otherwise, normal keyboards are fine, don't worry.

Idon't know what that mean either

Would you type back to me.