"held in bondage under the elemental principles of the world" (4:3). What are the elemental principles?

The chapter names them twice. "So we also, when we were children, were held in bondage under the elemental principles of the world." (4:3). And it asks, "why do you turn back again to the weak and miserable elemental principles, to which you desire to be in bondage all over again?" (4:9). The Greek word is the same in both verses, and Strong's gives it as "something orderly in arrangement, i.e. (by implication) a serial (basal, fundamental, initial) constituent (literally), proposition (figuratively)". The chapter says no more of what they are than these words, and these notes don't either. Nor do they say whom the chapter's "we" (4:3) and "you" (4:9) name.