What are the types of frames in photography? What are the different characteristics of each type of frame in portrait photography?

Frame refers to the size of the imaging unit. The standard size in a 135mm camera system (which includes DSLRs and side-by-sides, etc.) is 24mm*36mm, which is the size of traditional 135mm film.

In the digital camera world, smaller imaging units are used in the civilian or quasi-professional world due to the high cost of manufacturing large imaging units (CMOS or CCD). High-end models use the same size (24mm*36mm) imaging unit (CMOS or CCD) as traditional film, and we call such models full-frame or full-size cameras. Low-end models use imaging units smaller than this size, the general size of the imaging unit used by the digital SLR camera in 15mm * 23mm or so (each manufacturer varies slightly), we call this size of the SLR camera APS-C format. APS this name also comes from the field of traditional film, more than a decade ago, film manufacturers used to produce a smaller size of film, film could produce indexed photos, and this film was called APS film. Since the size of the imaging unit of a low-end DSLR is similar to the size of traditional APS film, it is called APS format. As for the APS-C name is because there is a less common imaging unit size slightly larger than the APS-C size, but smaller than the full frame, called APS-H, so there is a distinction. APS-H format cameras are relatively rare, Canon's 1D series of cameras, and Leica's M8 side-axis digital camera are used in this size.