A retriever is an interface that returns documents given an unstructured query. So it is more general than a vector store.

A retriever does not need to be able to store documents; it only needs to return (or retrieve) them.

Thus, retrievers accept a string query as input and return a list of document objects as output.

Developers can create retrievers for vector stores. However, the retrievers are broad enough to include Wikipedia search or Amazon Kendra.

Note that you can develop a retriever with a development framework (e.g., LangChain) and use it with any vector store that the development framework supports.