file system
/bin - binary files for terminal commands and core utilities 
/boot - GRUB and files needed for boot - may be located on a separate partition 
/cdrom - optical drive might be mounted here 
/dev - devices - hard drives are mounted here, and sometimes other devices 
/etc - configuration files, e.g. for SSH or installed applications 
/home - where user folders are stored (~) 
/lib, /lib32, /lib64- libraries - files used for installed applications; somewhat comparable to Program Files on Windows 
/media - where external devices like flash drives might be mounted 
/mnt - another place external devices might be mounted, as well as remote folders 
/opt - “optional software for the system” ?? 
/proc - processes - stuff used for the kernel to communicate with the running processes (?) 
/root - user account for the root user; its equivalent of home 
/run - a place where flash drives etc might automatically mount 
/sbin - similar to bin but for commands that can only be run by root or superuser 
/snap - where downloaded snap apps live 
/tmp - temporary files, usually deleted when system shuts down 
/usr - user - utilities shared between users 
/var - variable - system logs and other data, e.g. apache uses it as a default storage location 
swapfile - the system swap (extra memory for when RAM is maxed out or whatever)