Salesforce DX Developer Guide
jNote: This release is in preview. Features described here don’t become generally available until the latest general availability date that Salesforce announces for this release. Before then, and where features are noted as beta, pilot, or developer preview, we can’t guarantee general availability within any particular time frame or at all. Make your purchase decisions only on the basis of generally available products and features.
Develop Unlocked Packages
A package is a top-level container that holds important details about the app or
package: the package name, description, and associated namespace.
You supply the package details in the package descriptor section of your sfdx-project.json project configuration file.