When smoking ribs what is the 3-2-1 or the 3-2-2 method refer to?
TLDR;

This method is used many professionals for smoking ribs. 

Each number signifies the number of hours per phase.

Smoke as normal for 3 hours, followed by 2 hours cooking wrapped in foil, and finally 1 more hour unwrapped and finish with bbq sauce and/or on direct flame for appearance.

Unabridged version

Three

The first phase is the smoking phase. The meat should smoke for 3 hours to develop the right amount of smoke.

Two

This phase involves wrapping it in a foil. This phase is when one braises the ribs so that the texture of the ribs is tender. Usually a liquid is involved here. Typically, some use apple juice or vinegar. The braising liquid is typically an acid.

One or Two

The final phase is appearance. During this phase one cooks the ribs so they have this perfect char on it. This can last from half an hour to two hours depending on the size of the portion or one's preferred doneness. The purpose of it to simply get some char on it. Some finish this phase with bbq sauce on a grill.

Variances

Baby back ribs on the other hand sometimes utilize a 2-2-1 method; because of the size of the portion. It's not an exact science.

Sources:


About.com
Youtube - Traeger 3-2-1 ribs
Youtube - 3-2-1 explained