What does MacBook startup disk Macintosh HD mean? Some are startup disks are ssd (solid state drives)? What's the difference?

Macintosh (Macintosh) is the official name of Apple Computer, Macbook beginning Mac, is the abbreviation of Macintosh is also the first three letters Mac, Macintosh HD is the Macintosh computer hard disk, meaning that this is a piece of hard disk in the Macintosh computer. As for what you said SSD, called solid state drive is a hard disk hardware. macintosh can run on ordinary mechanical disks, can also run on SSD, so Macintosh HD can be both mechanical hard disk, can also be SSD. so your question, Macintosh HD and the SSD behind is not a concept of things.