Scratch Orgs are a central feature of Salesforce DX. It is source driven. It is used in disposable deployment of Salesforce code and metadata. It can shre scratch org config file with team mates. It works great for temporary deployment; for peer-review and test coverage/automation. Doesn't include production data. It is fully configurable, allowing developers to emulate different Salesforce editions with different features and preferences.
A page to guide you on your Salesforce journey. Wishing you the best.