LODs Question

I generally considered myself somewhat knowledgable about mods and cc. No expert, to be sure. But I knew enough I rarely was stumped but things have gone and got technical on me and I'm stumped.

I found an amazing CC Creator, and they keep listing "All LODs" on their CAS items. What does that mean, exactly? I want to know what I'm putting in my game beyond "oh, it's pretty". You know?