Throughout the codebase and design for internal transactions, we have been using a wide range of terms to refer to sessions started by an external client and sessions are started by a router to run transactions on behalf of a client. Those terms include external/internal/non-internal sessions, child/parent sessions, logical/transaction sessions, internal sessions for retryable/non-retryable write etc. The lack of formal terminology has made it difficult for us to write clear code. For example, the name of this _isInternalSession() method is misleading since it is possible for an internally started session to not have a parent session. This ticket to unify the naming and investigate if there is any bug caused by the existing ambiguity.