A?scratch org?is a dedicated, configurable, and short-term Salesforce environment that you can quickly spin up when starting a new project, a new feature branch, or a feature test.
A?Developer Hub (Dev Hub)?is the main Salesforce org that you and your team use to create and manage your scratch orgs.
After you enable Dev Hub in your org, you can’t disable it.
Activate Developer Hub
1 Launch your Trailhead Playground.
2 Click and select?Setup.
3 From Setup, enter?Dev Hub?in the Quick Find box and select Dev Hub.
4 To enable Dev Hub, click?Enable.