Example: "A foul odor"
Having a bad smell.
Example: "She was hesitant to remove her shoes, as her socks were rather smelly."
Having a quality that arouses suspicion.
Example: "The detective read the documents and thought, "something sure is smelly about this case.""
(in extreme programming) having signs that suggest a design problem; having a code smell.
Example: "That smelly code needs to be refactored."