DDO

Short definition from Wiktionary

Proper noun

1. 1
   Initialism of David Dunlap Observatory.
2. 2
   Initialism of Dollard-des-Ormeaux, a municipality in the province of Quebec, Canada.

Noun

1. 1
   Initialism of dynamic drive overlay, a type of computer software; a form of driver.
2. 2
   Initialism of designated detention officer.