This indicates the size/version of the image. _n usually stands for "normal" size. _s stands for "square" (thumbnail). _o stands for "original" (high resolution). 🛠️ How to Trace the Image
Historically, this often represented a unique image ID or a "photo ID." 88183129_233141317720418_1868439792004099529_n.jpg
This is a signature or checksum used by the CDN to verify the file and manage its distribution. This indicates the size/version of the image