Basically, it's smoking a cigar before lighting it. If you clip a cigar and put it in your mouth, then suck air through it before you light up, you can taste the tobacco inside. The flavor won't be the same as a burning cigar, but it will hint at the taste to come.
Who in the world would puff an unlit cigar? It's a common practice among those in the cigar industry. A cold taste, as it's known, can reveal certain qualities about a cigar. Especially spicy blends will have a kick, milder blends will taste neutral and cigars with young, raw tobacco may have offensive flavor in a cold taste.
Of course, we would never judge a cigar until after it's smoked. But a cold taste is an insider's way of getting a sneak preview, before you light.