What is foxing on book pages?

Answer 1

According to Book World, "spotting and/or browning" on the pages, is called "foxing." So far, that's all I've come up with. Which begs the question: Does this include the "age tanning" at the edges of the pages? According to ABOOKSEARCH.COM re: book foxing * foxing or foxed. Relatively light brown spotting on the pages of a book often caused by the chemical make-up of the paper itself or its sizing. Sometimes this can be heavily foxed to the point of obscuring some words of the text or lessening the enjoyment of plates, but usually it is a case of light foxing which is often considered a natural occurrence.