Spiderman vs. Firelord, or SvFL, is a shorthand that refers to any time when a character performs a feat that their powers and skills should be blatantly insufficient for, and is not repeated or is rarely repeated again relative to the character's overall established career, as well as the character's opponents' established showings. In statistical terms, it is an outlier, something that is radically beyond the character's established capabilities.
For example, Spiderman defeating a herald of Galactus is a case of the SvFL exemption; however, Batman being able to sneak up on Superman is not because he has done so frequently under different writers.
For standard CBR fights, feats considered to fall under the SvFL exemption are not valid. Likewise, examples of writing which go against firmly set canon are also ignored. For example, in Larry Hama's run of Batman and Grell's run of Iron Man, both characters were out of character and did things very much against established canon; therefore those runs are disregarded.