Scratch Org in Salesforce helps Source Driven Development.
The scratch org is a source-driven and disposable deployment of Salesforce code and metadata, made for developers and automation (CI/CD). A scratch org is fully configurable, allowing developers to emulate different Salesforce editions with different features and preferences.
Scratch Org Expiry:
Specify the scratch org’s duration, which indicates when the scratch org expires (in days).
sfdx force:org:create -f config/project-scratch-def.json --durationdays 30
Additional information - https://developer.salesforce.com/docs/atlas.en-us.sfdx_dev.meta/sfdx_dev/sfdx_dev_scratch_orgs.htm
To build a sample scratch org, check https://developer.salesforce.com/docs/atlas.en-us.sfdx_dev.meta/sfdx_dev/sfdx_dev_scratch_orgs_def_file.htm
