Green’s Dictionary of Slang

park n.¹

1. a prison or its yard.

1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 132: The Park is also the rules or privileged circuit round the king’s-bench or fleet . ‘The park is well stocked,’ when many prisoners have obtained the rules.
1824		History of Gaming Houses & Gamesters 47: In the Fleet-prison and around it, did our so-called Captain reside nearly twenty years, and it was he who set the name park upon the pace in which the rulers were circumscribed.
1832		Satirist (London) 25 Nov. 384/2: This place overlooks ‘the park,’ vulgo, the yard, where I beheld about two hundred persons who had passed their noviciate.
1847–81		Halliwell Dict. Archaic and Provincial Words II 605/1: Park [...] Slang term for a prison. York.

2. (UK black/gang) one’s home area.

2018-20

T. Thorne (ed.) ‘Drill Slang Glossary’ at Forensic Linguistic Databank 🌐 Park(s) – local area(s).

SE in slang uses

In compounds

park palings (n.) (also park railings) [SE palings, a fence/railings, i.e. resemblance]

1. the teeth.

1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 64: park railing The teeth.

2. a neck of mutton.

1937–84

Partridge DSUE (1984) 855/1: from ca. 1880.