A whiff can mean the hint of something you smell. When you drive past the sewage treatment plant and suddenly roll up your car windows, it's usually because you've gotten a whiff of the plant's special odor.
Whiff can be used as either a noun or verb, and it implies a brief or small puff or sniff. A person can have "a whiff of the exotic," which means they are living like the rest of us, but there is a little something about them that seems foreign or different. Sometimes, of course, odors are so overpowering that a small sniff is all you need: "Take a whiff of this," your friend might say to you, holding out a carton of sour milk. In that case, one whiff will be more than enough.