Simply known as ventilation system for removing any kind of smell from the premises to get a refresh environment. You can say odor control is type of fragrance.
The odor can be a reason from anywhere, your indoor plants, kitchen, Toilets, Roof, Celling, furniture, your closet or any other way to make annoying odor, may be from your pets and animal part. The odor can also a reason to attract attention of unwanted people.
Now a days in modern construction, the odor system is combining with ventilation (for unpleasant and pleasant odor),in general terms odor has a negative impression, but it can be pleasant as well which is hygiene free.