Beatmatching -- Speeding up and slowing down an incoming music track so that it plays at the same speed as the outgoing track. "A DJ usually has to use his hands to 'push' or 'pull back' on the record a bit," says Mr. Tan, "since it's very difficult to get the track to be exactly the same speed."
Scratching -- A turntable mix technique that involves moving the record back and forth by hand with the phono cartridge in the playing position, creating a variety of rhythmic sound patterns.
Slider -- Any electronic control that moves up and down. Those that control sound volume are more often known as 'faders.' The most notable slider that's not a fader is the 'pitch control slider' on turntables and some CD players. This allows one to change the speed of the record or CD, which is very important when trying to beatmatch.
Slipmat -- A circular piece of felt exactly the same size as a 12" vinyl record. It replaces the rubber mat on the turntable, allowing one to stop the record without stopping the motor on the turntable.
Turntablism -- The art of using a record player's turntable as a musical instrument, by making new sounds come from records.
Trainspotting -- Refers to the practice of going to a club for the primary purpose of figuring out what track the DJ is playing, as quickly as possible. "There are some really good DJs who can hear a few beats and know which track is next, or can hear the incoming track even while it's mixed in at a very low volume," says Mr. Tan. Recognition of and identification of a sample (a short snippet of sound) is another kind of trainspotting.
A version of this article appeared in MIT Tech Talk on February 10, 1999.