What is MOV?
MOV is QuickTime's container - what iPhones and Macs record. The open secret is that MP4 was standardised *from* it, so the two share their internal structure almost exactly, and reading one is reading the other. Writing a true MOV is another matter, which is why it converts from here but not to.
What is AAC?
AAC is MP3's designated successor and the audio in most video: YouTube, streaming services, broadcast and virtually every MP4. At a given bitrate it beats MP3 audibly, particularly below 128 kbps, and every phone and browser decodes it.