> ## Documentation Index
> Fetch the complete documentation index at: https://help.qrtub.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Key Concepts

> One or two sentences each on Collection, Item, Link, Page and Media, and which page owns the full explanation of each.

QRtub has five nouns. None of them require each other to exist — a Link can be printed before
any Item exists, and a Page can be built before any code opens it — so this page defines each
one and points to the page that owns it.

## Collection

A Collection groups Items that share one field schema, one link-generation rule, one scan
behavior, and one page template. It belongs to a team, and every Item belongs to exactly one
Collection. In URL templates and conditions, the namespace for Collection values is still
`collection.` — write `{{collection.name}}`, because `collection.name` returns an empty string with no
error. See [What Is a Collection?](/collections/overview).

## Item

An Item is the individual record a Collection tracks: one machine, one room, one product, one
extinguisher. What data it holds is decided by its Collection's fields, and it can carry one
or more Links. See [What Is an Item?](/items/overview) and
[Core Fields vs. Custom Fields](/fields/core-vs-custom).

## Link

A Link is a QRtub-managed URL, like `qrtub.com/r/x5fgd`, that resolves to a destination. A QR
code is one way to encode it — an NFC tag or a typed address work the same way. Links belong
to the team rather than to a Collection, so any Link can be assigned to any Item the team
owns, or to nothing at all. See [What a Link Is](/links/what-a-link-is).

## Page

A Page is the mobile screen a Link can open, holding one or more Destinations for the person
scanning to choose from, and built in the Page Editor. A Link that skips the Page and
redirects straight to a single Destination is in Direct Mode; a Link that opens a Page is in
Page Mode. See [Pages Overview](/pages/pages-overview) and
[Direct Mode vs. Page Mode](/pages/direct-mode-vs-page-mode).

## Media

Media is the physical thing the QR code lives on — a vinyl sticker, an engraved plaque, a
sign, an NFC chip — with a lifecycle of its own, often longer than the Item it is attached to.
QRtub tracks production runs as print batches; it does not keep a per-code record of material,
cost, or installation location. See [What Is Media?](/media/what-is-media) and
[Print Batches](/print-batches/overview).

## Related

* [Creating Your First Link](/creating-your-first-link) — these five in one worked example
* [The Print-First Workflow](/print-first/overview) — why printing before the data exists is normal here
* [What Is a Destination?](/destinations/what-is-a-destination) — where a scan actually ends up