Novel, light novel, web novel

Novel is a broad term referring to self-contained prose released in "book" format ("" because it's not necessarily physical book), that encompasses both LN and WN.

LN is Japanese-originating subtype of novel, that you could think of as novel released in manga-like way - it's released in cheap booklets, or posted piece by piece in cheap magazines, either way it often carries undertone of mass production - I'm not referring to volume of sales, but author's productivity. LN authors are expected to either continue soon, or release something new, even at the cost of quality. Closest western equivalent would be pulp novel, but it's important to note manga influence.

WN is just a novel that is published on net. However, typically when someone around here uses the term, they are typically referring to web release in bite-sized chunks, perfectly sized for a blog entry. This is not textbook definition, a lot things could be considered as web novel as long as it is on the internet or a web.