Lax means loose, careless, or not strict enough. When rules are lax, they're not enforced firmly. When someone's behavior is lax, they're not paying enough attention or being careful enough.

A teacher with lax classroom management might let students talk during lessons or turn in homework whenever they feel like it. Airport security can't afford to be lax because missing even one dangerous item could put everyone at risk. If you're lax about brushing your teeth, you might end up with cavities.

The word often suggests that someone should be more careful or strict but isn't. A coach might tell their team, “We've gotten lax about practicing the fundamentals,” meaning they've become sloppy about the basics. Parents might worry their teenager is getting lax about curfew, coming home later and later without good reasons.

The opposite of lax is strict, rigorous, or stringent. While being too strict can cause problems, being lax can lead to sloppiness, mistakes, or things falling apart.