What does "LBS" mean in the context of WAI?

There are several identifiers in WAI containing "LBS":

• Network.Wai.responseLBS:: Status -> ResponseHeaders -> ByteString -> Response

• -- | Store uploaded files in memory
lbsBackEnd:: Monad m => ignored1 -> ignored2 -> m S.ByteString -> m L.ByteString

I can't find anything in the WAI documentation that mentions "LBS". What does it mean?

From the Hackage documentation:

The overriding design principles here are performance and generality. To address performance, this library is built on top of the conduit and blaze-builder packages. The advantages of conduits over lazy IO have been debated elsewhere and so will not be addressed here. However, helper functions like responseLBS allow you to continue using lazy IO if you so desire.

so, yes, LBS does stand for Lazy ByteString.