Glossary

Mount

Attaching a filesystem to a directory in the tree.

Mounting makes a storage device (or network share, or virtual filesystem) accessible at a chosen directory, called its mount point. After mounting a disk at /data, everything under /data lives on that disk while the rest of the tree is unaffected.

This is why Linux has no drive letters, and why df lists filesystems by mount point. Permanent mounts are declared in /etc/fstab; lsblk shows devices and where each is currently mounted.

See it in practice

$ lsblk && df -h /

Which devices exist and where each is attached, then how full the filesystem holding / actually is.

Where you'll meet it