Term

What is the term when one uses words like 'tonite' instead of 'tonight' or 'luv' instead of 'love' in slang terms?

[Tdol]

I've never heard of a specific term for these colloquial spellings.

[Tdol]

I've had a hunt around and the only term I have found is Variant Spellings, which is a broader term that would include British and American spellings:
"Lite" is used in published, edited matter, and basically only for one quite specialized meaning, "having fewer calories," or figuratively, "having less substance." But "lite" really isn't used in print for other meanings of "light"; in fact, "lite" is emerging as an entity on its own, with a literal meaning it got from "light" (fewer calories) and has, as its own word now, developed an additional figurative meaning.

The "American Heritage Dictionary," 3rd Edition has an entry for "lite" which reads: _
lite (l i t), _adj._ _Slang._ Having less substance or
weight or fewer calories than something else: _"lite
music, shimmering on the surface and squishy soft at
the core"_ (Mother Jones) [Alteration of LIGHT 2.]

(http://www.barnsdle.demon.co.uk/spell/varsp.html)

[Tdol]

Some people use the term 'deviant' language use, where rules are deliberately twisted for effect, so these spellings could also be called 'deviant spellings'.