"The This and the That" is an expression used to summarize
key points in a
conversation without actually saying what "this" is or what "that" is. Using the phrase assumes the audience knows what "this and the that" refers to, or they can infer from the rest of the conversation. Can expedite a conversation rapidly to get to the point.
It is customary to follow the
phase "a this and the that" with the "that and the this," - everyone gets it.