DNF

Did Not Finish (racing)    
Duke Nukem Forever
Digital National Framework (UK)
Dungeon and Fighter (video game)
Do Not Forget
Does Not Follow (mathematical proofs)
Dynamic No Fins (swimming)
Domain Name Forum
Data Not Found
Digital Noise Filter
Danmarks Nationale Front (Danish: Denmark’s National Front)
Disjunctive/Disjoint Normal Form
Down ‘n Floundering (racing)
Second Disjunctive Normal Form
Domain Name Finder
Did Not Find
Does Not Function
Do Not Forward
Do Not Freeze (USAP)
Do Not Fax
Do Not Fix (software bug)
.NET Framework (Microsoft)
Direction Nationale des Formations (French: National Directorate of Training)
Deep Neck Flexor
Defense Nuclear Facilities
Deschutes National Forest (Oregon)
Dominant-Negative Form (genetics)
Droits des Non Fumeurs (French: Non-Smokers Rights)
Dynamic Network Factory, Inc.