What is a folder?

A folder is exactly what it sounds like: a labeled container that holds files. Same idea as the manila folder in a filing cabinet, except it can also hold other folders.

That last part is the whole trick.

Boxes inside boxes

A folder can contain files. A folder can also contain other folders. Those folders can contain more folders. Keep going as long as you like:

Documents/
├── work/
│   ├── 2024/
│   │   └── report.pdf
│   └── 2025/
│       └── notes.txt
└── personal/
    ├── photos/
    │   └── beach.jpg
    └── recipes/
        └── pasta.txt

Documents is a folder. Inside it: two more folders (work, personal). Inside work: two more folders. Inside those: actual files.

This branching shape — boxes inside boxes — is called a tree. Your whole computer is one giant tree of folders, with files hanging off the branches.

A folder is not a place

Here’s the part people miss: a folder isn’t really a location on your hard drive. It’s a label. A way of grouping files so you (and your computer) can find them.

The bytes of beach.jpg live somewhere on your physical disk. The folder photos is just a note that says “these files belong together, call this group photos.” Move the file to a different folder and the bytes don’t physically move much — the label just changes.

You don’t need to remember that. But it’s why “moving” a file from Downloads to Documents is instant for files on the same disk — nothing big actually moves.

”Folder” or “directory”?

Same thing. Folder is the friendly word, used in Finder, File Explorer, and most documentation aimed at people. Directory is the older, more technical word — what the terminal uses, what programmers say.

When you see cd (we’ll meet it soon), the d stands for directory. Same idea, different hat.

What’s next

If everything is files and folders, how do you tell the computer which file you mean? You give it an address. That address is called a path, and that’s the next lesson — but first, a detour through the most misunderstood thing on a computer: apps.