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

# Key concepts

> Important terminology and ideas

In this section, find out or remind yourself of the most important terms and concepts.

<CardGroup cols={3}>
  <Card title="Products and plans" href="/legacy/subscriptions/concepts/products-plans" cta="Read more">
    Users subscribe to one of the plans of a product
  </Card>

  <Card title="Subscription lifecycle and timeline" href="/legacy/subscriptions/concepts/lifecycle" cta="Read more">
    States, events, and phase transitions
  </Card>

  <Card title="Billing periods" href="/legacy/subscriptions/concepts/billing-periods" cta="Read more">
    How often users are charged
  </Card>

  <Card title="Renewal" href="/legacy/subscriptions/concepts/renewal" cta="Read more">
    What does "renewal" mean?
  </Card>

  <Card title="Conversion" href="/legacy/subscriptions/concepts/conversion" cta="Read more">
    What does "conversion" mean?
  </Card>

  <Card title="Idempotency" href="/legacy/subscriptions/concepts/idempotency" cta="Read more">
    Avoiding accidental duplications
  </Card>
</CardGroup>

<Card title="FAQ" href="/legacy/subscriptions/faq/index" cta="Read more">
  Here are some frequently asked questions about the Bango Subscriptions API.
</Card>