What are the "realms" or "planes of existence"?

Various suttas mention various 'planes' or 'levels' or 'realms' of existence; for example: > **[The Thirty-one Planes of Existence](http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html)** > > Scattered throughout the suttas are references to as many as > thirty-one distinct "planes" or "realms" of existence into which > beings can be reborn during their long wandering through samsara. > These range from the extraordinarily grim and painful hell realms all > the way up to the most exquisitely refined and blissful heaven realms. > Existence in every realm is temporary; in Buddhist cosmology there is > no eternal heaven or hell. [etc.] > > The realms of existence are customarily divided into three distinct > "worlds" (loka), listed here in descending order of refinement: > > - The Immaterial World (arupa-loka). Consists of four realms that are > accessible to those who pass away while meditating in the formless > jhanas. > > - The Fine-Material World (rupa-loka). Consists of sixteen > realms [etc.] > > - The Sensuous World (kama-loka). Consists of eleven realms [etc.] > > The information on this page was assembled from a variety of sources. > In the interests of economizing space I have not attributed each fact > to its respective source. I don't want to ask for a precise list, but how or what should I understanding these realms are? I have heard several versions now of what "levels of existence" are: - Some say it is like physical, or is it mental (psychological), biomes in this universe? - Others say it is other universes or even other dimensions?