Linux Filesystem Hierarchy Standard (FHS)

/bin : binaries to run fundamental Linux functions
/boot : boot partition
/cdrom : legacy mounting point
/dev : mount points
/etc : etcetera, stores configurations system-wide
/home : user folders (desktops, downloads, medias)
/lib : libraries
/lib32 : i386 libraries
/lib64 : x64 libraries
/media : mount points for external and secondary devices (e.g. USB thumb drives)
/mnt : mount points for devices that are manually configured by users
/opt : optional folders for manually installed software from various vendors
/proc : contains system processes or pseudo-files (e.g. cat /proc/cpuinfo)
/root : contains files that require root permissions to access, reserved for root user as its dedicated home folder
/run : stores run-time processes
/sbin : system binaries, similar to /bin with higher restrictions that are reserved for sudo access
/snap : snap packages or self contained apps
/srv : service directory, typically contains web service files
/sys : system folder, pseudo-files that are generated at boot time
/tmp : temp directory, system uses to store editing-in-progress files
/usr : user applications, non-system apps
/var : variables, holds directories and files are expected to grow in size