What does Boot Leg mean?
A style of jeans that is characterized by having wide leg openings, which were originally created as to allow for the ability of the jean to fit over boots.
Heddels explains Boot Leg
Boot legs, or boot cut jeans, were so named for their cut designed to allow for a pair a boots underneath the pants. The style evolved from the pants that sailors originally wore that were easy to pull on over boots, to roll up while swabbing the deck, and to remove when wet. The term “boot cut” arose in the late 1980s to distinguish the style from the more flared bell bottoms of the hippie movement of the 1960s and 1970s. Today, boot cut jeans are normally slimmer at the thighs and knees with a small to moderate flare towards the bottom.
Here is an example of boot leg: