Green’s Dictionary of Slang

(rap music) two turntables, as used by a hip-hop DJ.

1999		Hip-Hop Connection Aug. 21: 1s and 2s. Turntables. The musical foundation of hip-hop, no self respecting or would-be deejay is seen without turntable 1 and turntable 2.
2000		Guardian Guide 1–6 Jan. 18: Takin’ over the ones’n’twos from my nigga, Jacques Peretti.
2002		Tony Touch ‘Live from Club 1’ 🎵 This is Tony Touch on the one and two.
2006		DJ Cameo on 1Xtra 8 Apr. [BBC radio] On the ones and twos, on the decks.