copyleft
/ˈkɒpiˌlɛft/
UncommonA licensing approach that lets anyone use, modify, and share code as long as derivatives stay under the same license.
Often used approvingly by open-source advocates and skeptically by companies who want to commercialize without sharing back.
Real-world examples4 examples
| # | Example | What it means | Source |
|---|---|---|---|
| 01 | they can't ship that in their product, it's copyleft | The library's license would force them to open their own code. | reddit, 2023 |
| 02 | copyleft is the whole point. you share, i share, everyone shares. | The reciprocal nature of copyleft is a feature, not a bug. | x, 2024 |
| 03 | legal said no because the dependency is copyleft and we're not open sourcing the product | Corporate legal blocked the library for license compatibility reasons. | reddit, 2022 |
| 04 | switched from MIT to AGPL. going full copyleft. | The project owner changed to a stronger share-alike license. | x, 2023 |
Use it when
- Describing a software license that requires derivative works to stay open.
- Explaining why a company can't use a particular library in a closed product.
- Discussing GPL, LGPL, AGPL, or similar licenses.
- Contrasting with permissive licenses like MIT or Apache.
Do not use it when
- You just mean something is free to use.Use “open-source” instead.
- You mean someone is against copyright entirely.Use “anti-copyright” instead.
Variations and related forms
Copyleft vs open-source
copyleft
Copyleft is a specific licensing strategy within open source that requires derivatives to stay open.
VS
open-source
Open source is a broader category that includes both copyleft and permissive licenses.
Origin and context
Coined by Richard Stallman in the 1980s as a play on copyright. The GPL was the first copyleft license, designed to ensure software freedom could not be revoked by downstream users.
- First seen
- 1980s
- Confidence
- high
Cite this page
Use this stable URL to reference the entry.
https://slang.fyi/copyleftUpdated: 2026-08-28License: CC BY 4.0