Green’s Dictionary of Slang

(US) describing a hotel offering single rooms occupancy.

1971		R.D. Pharr S.R.O. (1998) 12: The place had long since been cut up into a single-room occupancy hotel [...] But no hotel operator [...] has ever heeded the meaning or the letter of these laws for S.R.O.s.
1995		J. Stahl Permanent Midnight 345: A seedy, bathroom-down-the-hall, ‘No Guests After Ten’ SRO.
2006		D. Winslow Winter of Frankie Machine (2007) 91: A rough neighborhood of SRO hotels, strip clubs and porno shops.
2013		J. Stahl Happy Mutant Baby Pills 19: I have enough to stay at this hotel, the Grandee (an SRO) for a couple more weeks.
2022		I. Fitzgerald Dirtbag, Massachusetts 100: SRO rooms, with shared bathrooms at the end of each hall.