Green’s Dictionary of Slang

squad n.

1. a group of prostitutes.

[UK]M. Leeson Memoirs (1995) III 174: On her joining my squad, she told me in what elegance the printer had kept her.

2. (US black) a gang or group of friends.

[[UK] Burns To James Smith in Works (1842) 24/1: Nae ferly tho ye do despise The hairum-scarum, ram-stam boys, The rattling squad].
[US]D. Burke Street Talk 2 50: That’s my squad over there.
[UK]L. Theroux Call of the Weird (2006) 192: They would send a goon squad to [...] finish him off ‘execution-style with a dirty twenty-two’.
[US]‘Grandmaster Flash’ Adventures 215: [of a hip-hop crew] ‘My man's name is Chuck D,’ he said, ‘and the squad’s Public Enemy.’.
[US]C. Eble (ed.) UNC-CH Campus Sl. Spring 2016.

3. (US police) a police car.

[US]R. Cooley When Corruption Was King 45: When I rode the squad by myself, I [...] made some unbelievable arrests.
[US]J.A. Juarez Brotherhood of Corruption 66: I cuffed him, led him back to the squad, and put him in the rear seat.

In derivatives

squaddy (adv.)

involving a large number of people.

Stormzy ‘Shut Up’ 🎵 They roll deep, I roll squaddy / Got about 25 goons in my posse.

In phrases

squad up (v.)

(US campus) to do something as a group.

[US]C. Eble (ed.) UNC-CH Campus Sl. Spring 2016 9: SQUAD UP — cooperate with members of one’s group to achieve a goal: ‘Let’s squad up this afternoon to go to the mall’.