Solenoid = Little electric gadget with an inductive coil that moves a piston up and down depending on polarity.
Basically on a marker it does the same sort of thing as a 3 way on a cocker, but electronically. Hence the E-blade has a solenoid on the front.
Don't worry about them too much, just don't freeze them, or feed them more than 200 psi. And keep them greasy!!!