> ## Documentation Index
> Fetch the complete documentation index at: https://next-developers.opencard.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Glossary

> OpenCard glossary — EMS, account, organization, billing, card holder, identity, TPA, PDPC, transaction state, card issuer, receipt provider, webhook defined.

| Term                  | What it means                                                                                                                          |
| --------------------- | -------------------------------------------------------------------------------------------------------------------------------------- |
| **EMS**               | Expense Management System — software for corporate card spend, expenses, and receipts.                                                 |
| **Account**           | Your Expense Management System partner account. Top of the hierarchy.                                                                  |
| **Organization**      | Your end-client. You set `reference_id`. Has webhooks + card holders.                                                                  |
| **Billing**           | Invoice recipient + roll-up. Organizations with the same `billing_id` appear as **one line** on the invoice you receive from OpenCard. |
| **Card Holder**       | Individual whose transactions you receive. You set `reference_id`.                                                                     |
| **Identity**          | Physical person in OpenCard (SSN via eID). Has cards. Use `identity_id` for instant onboarding.                                        |
| **TPA**               | Transaction Processing Authorization. Company-level legal agreement.                                                                   |
| **PDPC**              | Personal Data Processing Consent. Individual GDPR consent.                                                                             |
| **Transaction**       | One purchase. ID stays same across all states.                                                                                         |
| **Transaction State** | Snapshot: `authorized`, `cleared`, `deleted`, `invoiced`.                                                                              |
| **Card Issuer**       | Bank or card program. Delivers transactions via the Issuer API; may also use `receipts.opencard.io` for digital receipt matching.      |
| **Receipt Provider**  | Collects receipts from merchants and delivers them to OpenCard. OpenCard forwards enriched data to Expense Management Systems.         |
| **Webhook**           | HTTP POST from OpenCard when stuff happens.                                                                                            |
| **Reference ID**      | Your string ID on orgs/cardholders. In every webhook.                                                                                  |
| **Challenge**         | Webhook verification handshake on setup.                                                                                               |
| **Scope**             | OAuth permission string like `webhooks-write`.                                                                                         |
| **CAID / MID**        | Merchant ID in receipt networks.                                                                                                       |
| **MCC**               | Merchant Category Code (ISO 18245).                                                                                                    |