What does WFQFN stand for?
Funny, ATMEL doesn't use WFQFN as a label. That attiny85 has a 20m1 package, which is based on the JEDEC MO-220 MLP, Otherwise known as QFN. At most, they reference it as WQFN, not WF.

And the W in WQFN stands for Very Very Thin (0.75mm in height). As opposed to VQFN, which is Very Thin (0.9mm). UQFN being the newest and thinest at this time (0.5mm).

Alternatively, WQFN and and UQFN are also known as TQFN and UTQFN. Depends on the manufacturer.