application/vnd.openxmlformats-officedocument.presentationml.presentation

PowerPoint's Office Open XML deck (ECMA-376, ISO/IEC 29500) — like its DOCX and XLSX siblings it is a zip of XML parts, so on the wire it is indistinguishable from any other zip until something opens it and finds ppt/presentation.xml. That shared container is why no signature is listed here: the PK bytes identify the wrapper, never the format. Mislabels usually reach for application/vnd.ms-powerpoint, the binary .ppt type, or plain application/octet-stream; both are common enough that consumers end up trusting the extension instead, which is exactly what media types were meant to avoid.

.ppsx, the open-straight-into-slideshow variant, is a separate type — application/vnd.openxmlformats-officedocument.presentationml.slideshow.

Defined by ECMA-376 — Office Open XML file formats · IANA registration. Registry facts from the IANA media-types registry via mime-db.