The title of the story is hard to parse, until one reads the first sentence:
Like a rental bike returned with a tire puncture, Ark woke up in a stranger’s apartment.
Ark is a person, and one in very curious circumstances indeed.
The circumstances under which Ark has become someone — something — that can be borrowed are not very pleasant. Cunningham’s story is a future-set SF story, and it’s not a hopeful future, but rather one rife with segregation, destruction of nature, and sordid hook-ups.
There was a lot going on in the story that I found difficult to keep track of or to hang together in a sensible story; I often felt like I was missing a necessary piece or two, trying to figure out who the various characters were and what exactly was going on — is Ark the one borrowing or the one who is being borrowed? Half-way through the story, I was still unsure, though by the — rather abrupt — end I had figured some things out. Certainly the complexities of the story merit reading it more than once, although both times through felt more edifying than educational.