the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form
"she loved the smell of roses"
Any smell, whether fragrant or offensive.
"The dog's bowl developed an odor that was neither particularly pleasant nor disgusting."
In plain English: An odor is any smell that you can detect with your nose, whether it smells good or bad.
"The strong odor from the garbage can filled up the entire hallway."
Usage: Use "odor" to refer to any distinct scent, though it is frequently used interchangeably with the more common word "smell." While both terms cover pleasant and unpleasant scents, "odor" often carries a slightly stronger connotation of being noticeable or pungent in everyday conversation.
The word entered English through the path of Middle and Anglo-Norman before arriving from Old French and its Latin ancestor, where it originally meant a scent or fragrance. While its meaning has narrowed in modern usage to often imply an unpleasant smell, this shift occurred gradually as speakers began associating strong odors specifically with bad smells rather than all scents equally.