The adjective / verb ratio is a mental tool that can be used for literary criticism. Notionally, it is the number of adjectives found in the story, divided by the number of verbs. (In actuality, no one would go to the trouble of computing the exact value. The measure is meant to be somewhat subjective) It can be used to diagnose problems related to poor balances of description and action.
A story with a high a/v ratio has too much description and not enough action. The reader will come to know the characters and the setting in great depth. The position of each leaf and the shifting of every emotion is expounded upon in great detail. But after a time the reader no longer cares because no one is doing anything! The action need not be physical. Emotional and ideological shifts can add excitement as well, so long as the situation is changing at a rate sufficient to hold the reader's attention.
A story with a low a/v ratio has a very different problem. The situation changes too fast and with too little supporting description. The result is confusion as the reader's mental model of the characters and settings diverge from the author's, leading to comments like: "Wait, what's he doing here? I thought he was still outside in the garden!". The reader no longer understands what is happening (but darned if there isn't a lot of it!) and gives up on the book.
Between the Mountain of Boredom and the Pit of Confusion lies the Valley of Good Storytelling. The problem is finding it.