What is "vanishing fraction"

Vanishing \Van"ish*ing\, a. & n. from Vanish, v.

Vanishing fraction (Math.), a fraction which reduces to the form 0/0 for a particular value of the variable which enters it, usually in consequence of the existence of a common factor in both terms of the fraction, which factor becomes 0 for this particular value of the variable.
--Math. Dict.

Vanishing line (Persp.), the intersection of the parallel of any original plane and picture; one of the lines converging to the vanishing point.

Vanishing point (Persp.), the point to which all parallel lines in the same plane tend in the representation.
--Gwilt.

Vanishing stress (Phon.), stress of voice upon the closing portion of a syllable.
--Rush.

n. (context math English) A fraction which reduces to the form $frac\{0\}\{0\}$ for a particular value of the variable which enters it, usually in consequence of the existence of a common factor in both terms of the fraction, which factor becomes 0 for this particular value of the variable.