Brahmas and Devas?

Are Brahmas and Devas the same thing in different levels or are they two entirely different beings. ---- I am asking this because if see the first teaching of Lord Buddha (Dhamma chakka pawaththana) there is a mentioning "Brahma Deva",yes both words used as a combination. Normally they are considered two kinds,here it is still the same but Brahmas have being attached to the Deva realm. Can someone explain?