The first five books/pentateuch is the torah, the tanakh is the whole of the old testament. The reason this is labelled ‘torah portion’ is because originally it was a year long cycle of weekly readings through the torah. This was then expanded to include a set of complimentary readings from the rest of the OT. Then finally relevant passages from the new testament were added to complete the picture. The original name just never got updated. (The talmud is a whole heap of discussions and writings about the scriptures and other stuff.)