Short description
Sometimes dependencies are so generic that you don't want to invest time in it and you can either buy them off the shelf or use a SaaS functionality.
You only oursource when there is enough competition in that market
Examples
Payment providers like stripe, paypal etc. Usermanagement, single sign-on like AWS or oath.com
Context
Use these at a strategic level when defining bounded context. When you want to seperate core domains from supporting and generic subdomains