The phrase "what is contained" is commonly used to refer to something that is included or held within a specific space or structure. Some synonyms for this phrase can include "contained materials," "inclusions," "contents," "enclosed items," or "incorporated elements." Additionally, terms like "inner workings," "internal components," or "hidden contents" can be used to describe what is contained within a particular object or system. Overall, there are many different ways to express the concept of what is contained, and choosing the right language depends on the specific context and purpose of the communication.