Industry Term for Missing/Floating/Lifted Pin on IC Package
What is typical for these types of packages is that the leadframes are ordered in and come in a flat stamped sheet like reel of metal, the leads are shaped and placed in the mold for the epoxy injection.  If you want to reuse an existing mold but want to leave out a pin or leg then you need to have a vestigal lead in there to prevent the epoxy from squeezing out during molding.  It is either than or get a new mold made.  Here is what a untrimmed lead frame looks like before forming (but for a different product/package type). 



I am unaware of what a generic term might be for this.  I've heard variously, dropped/missing/blank pin.  But I am sure it's not industry standard.