In the context of "I.Q. Tests for the High Range", "I.Q." is an abbreviation of "Intelligence Quantifier", and meant to approximate where a particular score belongs on the scale of adult intelligence. The word "Quantifier" is used instead of the common "Quotient" because I.Q., as currently computed, is in no way a "quotient", that is, an answer to the question "how often" (does the one fit into the other). The word "Quantifier" therefore fits the meaning better: a number quantifying an amount, either continuous or discrete.
It is striven for to make I.Q. approximately intervallic (linear), and objective, independent of age, sex, or population. I.Q. is not a true ratio scale in that it does not have an absolute and meaningful zero. It is attempted however to ascertain that a given I.Q. corresponds to the same intelligence level across candidates and across time (years, decades, centuries, eras).
It is important not to confuse I.Q. with childhood scores (either mental/biological age ratio scores or standard scores by age group), age-corrected or age-based scores for adults, estimated or quoted "I.Q."s of famous people or self-assumed "I.Q."s of megalomaniacs, each of which tend to be much higher than real I.Q.s. While it is true that "I.Q." started out as the ratio of a child's mental and biological age, this concept is meaningless and impossible for adults, and has even for children been abandoned decades ago.