Glossary
Microsoft AppSource
AppSource is Microsoft's marketplace for business applications, including SharePoint Framework solutions. Publishing there requires passing a free certification review run by Microsoft, which checks that the solution behaves, declares valid publisher metadata and does not let end users inject arbitrary script.
Presence in AppSource is a useful trust signal in an IT review: it raises the floor. It does not replace your own review, because the certification does not audit the vendor's backend, their subprocessors or how they handle data.
For vendors, the mandatory pieces are easy to get wrong: the package manifest must carry a publisher name, a website, a privacy URL and terms of use, and solutions exposing components in Teams must be tenant-scoped.