Definition
To go faster; to hurry up.
Origins
A shortened form of get the lead out of one's shoes (or one's pants). Here, lead refers to a very heavy metal, thus the expression means roughly to get rid of whatever is slowing one down and hurry up.
How People Actually Use It
to hurry up; to work or move faster; (pronounced like lead pencil) This expression can probably be loosely interpreted as removing dead weight from a vehicle so that it can travel faster.
"Bart Simpson: Come on Homer, get the lead out!"
Source: Urban Dictionary