The phrase "leg elastics" refers to stretchy bands or straps that go around someone's legs. They are commonly used to help hold socks or pants in place, or to provide support and compression for certain medical conditions. Full definition
The first layer of leg elastic hugs the leg to keep poop in, but should something slide past it, it gets caught by the second layer. (pootersdiapers.com)
Softbums makes an incredibly soft and trim diaper with adjustable leg elastic and fabulous aplix, making it a one size diaper that truly works well on a newborn. (theclothdiaperwhisperer.com)
The Simplex has rolled leg elastics to provide a snug but gentle fit around legs. (themamaknows.com)