Those parents who let their kids eat all their Halloween candy the night of October 31st? Their parenting style might be described as lax. A paperclip chain used as a bike lock? That's an example of lax security.
While contemplating the word lax, you may note that it's the same as the first syllable in laxative. This is not a coincidence: lax entered English as a noun describing a substance taken or administered to relax the bowels. Interestingly, the modern definition of lax is closer to the Latin source word, laxus — an adjective meaning "loose." Now, lax can refer to any phenomenon that is insufficiently stringent or so slack as to be basically ineffectual. For example, "The entire class performed incredibly well on the test, largely due to the sleepy professor's lax supervision."