What is this on my cat's skin?

[Sondos M]

She's been itching a lot lately so I shaved off her fur and found this underneath:

https://imgur.com/cKkpRRK

what could this possibly be?

She's an indoor cat, doesn't go outside and we have another cat in the house with no similar complaint

[Kay]

no direct experience, but my guess would be a healing abscess - these images look similar https://www.google.com/search?q=cat+abs ... 20&bih=910

letting the air in may help the healing process, and bathing in salt water to keep any infection at bay