"Speedrunning" is Reaching the end of the level as quickly as possible. In Duke Nukem 3d there are 2 different types of speedrunning; On The Xbox Live Arcade version, You can get the quickest time. (Time Trial Leaderboards) or the largest score for that level by finding all secrets on "Damn im Good" difficulty and finishing in the quickest time. (Single Player Leaderboards)
There are 2 variants to these Speedruns, "Pistol Start" and "Item Start". Pistol start is starting the level from the main menu whereas Item start is starting at previous levels to gather useful equipment such as Jetpack & Steroids for quicker times.
The Best Duke Speedrunners on the XBLA version are (in no particular order) Dysits, King Mamba 48, Helinkka, xBloodyWolf, KTILLA23, HaloJesse, SBMxRECOGNIZE, Peketeus, Slinky Ss, and Dingbell.
To view speedruns, access the leaderboard while signed into Xbox Live and Press Y on different Gamertags to see their Variation of a certain Level..
Note: The speedruns on Xbox Live are heavily segmented with the intent of achieving near perfect times that wouldn't be possible to pull off in single segment speedruns.
In 2007, the world record Duke Nukem 3D speedrun (viewable on Speed Demos Archive) is 20 minutes and 58 seconds set by Fernando 'Fernito' Calvo, who exploited many programming glitches.