The Microsoft Graph People API provides RESTful capabilities to discover People, through user behavioral patterns and fuzzy matching, who are relevant to a given user.
Microsoft Graph applications can use the People API to retrieve the people who are most relevant to a user. Relevance is determined by the user’s communication and collaboration patterns and business relationships. People can be local contacts, contacts from social networking or from an organization’s directory, and people from recent communications (such as email and Skype). Along with generating this insight, the People API also provides fuzzy matching search support and the ability to retrieve the list of users relevant to another user in the signed-in user's organization. The People API is particularly useful for people picking scenarios, such as composing an email or creating a meeting. For example, you can use the People API in email compose scenarios.
For more details on the MS Graph People API, see https://learn.microsoft.com/en-us/graph/people-example