A satta is any living being without at least the Sotapanna Anugami stage of Nibbana.
- Sotapanna Anugami is the “lowest” of the eight Noble Persons (Ariyas). All Ariyas are guaranteed to attain Nibbana (Arahanthood) within seven bhava (existences.)
- Any other living being (including all Devas and Brahmas) belong to the “satta” category.
- That is explained in the “Satta Sutta (SN 23.2)” you quoted. I have linked to the exact place in the sutta: “Rūpe kho, rādha, yo chando yo rāgo yā nandī yā taṇhā, tatra satto, tatra visatto, tasmā sattoti vuccati” OR “Anyone who has cravings for sensory inputs (rupa) is a “satta.”
- In the strict sense, only an Arahant is not a “satta.” However, all other Ariyas are guaranteed to attain Arahanthood within seven bhava (existences). Thus, an Ariya is usually not included in the category of “satta.”