taxi, n. — Green’s Dictionary of Slang

taxi n.

also taxi-bit

[New York cabs which displayed these figures, indicating their rates per mile, on the side]

1. (US) a sentence of 5 to 15 years.

1933		Ersine Und. and Prison Sl.
1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 220/2: Taxi-bit. (P) A five-to-fifteen-year prison sentence.

2. (N.Z. prison) one who carries contraband into prison.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 185/1: taxi n. = donkey.

In compounds

taxi-driver (n.)

(N.Z. prison) an officer with no specific job.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 185/1: taxi driver n. a prison officer, esp. one not assigned to any particular wing or set of duties.

taxi-surfing (n.)

riding on the roof of a moving taxicab.

2007

G. Carins Diary of a Legionnaire 194: Someone mentioned taxi surfing, and giving the driver some money not to pull over we took it in turns to climb out of the back window and onto the roof of the car .