Stakeholder interviews are conducted at the beginning of the UX process. Basically, you interview internal stakeholders who are directly involved in the feature you're working on.
Stakeholder interviews help you understand the problem from different perspectives and build trust with others on your team. The purpose is to glean each team member’s understanding of the problem, learn what they know, what they don’t know, their assumptions, what questions they want to see answered, and what constraints the project is under.
For example, early in the process, you might interview the developer who’s responsible for coding your solution. By talking to her, you discover that the feature is being built on a legacy codebase, which limits your design in some way. While this might hamper your designs, it’s super-valuable to know this up front so you can keep these constraints in mind. Make sure to include everyone who is directly involved in the project. Otherwise, you could end up designing something that is impossible to execute.
In our humble opinions, there's a better way to capture this information called “Framing the problem.”