Open Source is a cost-allocation system

The useful part

Open Source is usually described as a licensing model, a development model, or a production model. A proprietary vendor can tie access to payment: every license or subscription sold helps fund developers, security work, infrastructure, and releases. Payment is therefore not a condition of using or redistributing it, and those rights do not themselves provide a durable mechanism for funding production and maintenance.

How it works

• Costs are distributed across maintainers, employers, foundations, sponsors, and users.
• Because these costs are distributed rather than collected through a single transaction, they are harder to see and harder to fund.
• Drupal sites periodically contact updates.drupal.org to ask whether new versions of Drupal or any installed add-ons are available.
• Drupal calls these add-ons "contributed projects", such as modules and themes maintained by members of the community.

Details worth keeping

All three descriptions are useful, but they leave something out. Every Open Source ecosystem is also a cost-allocation system. Keeping software relevant and dependable requires people to write code, review contributions, prepare releases, investigate security reports, operate infrastructure, write documentation, answer questions, and support upgrades and migrations.