Why F-bounded polymorphism and F-bounded quantification are called, well, F-bounded
It appears that "F" does not stand for anything in particular: rather, it is the metavariable symbol that is used in the definition of F-bounded quantification. In the paper in which F-bounded quantification was introduced, F-Bounded Polymorphism for Object-Oriented Programming, the authors write:


  To solve this problem and related difficulties with other forms of recursive types we introduce a generalization of bounded quantification which we call F-bounded quantification, for want of better terminology. 


suggesting that they do not view the name as particularly descriptive. Later, when they define F-bounded quantification explicitly, they write:


  We say that a universally quantified type is F-bounded if it has the form
  $$\forall t \subseteq F[t] . \sigma$$
  where $F[t]$ is an expression, generally containing the type variable $t$.


As far as I can tell, the paper contains no other explanation and the most apparent explanation is that the "F" in the terminology is chosen to coincide with the symbol $F$ chosen, arbitrarily, for the definition.