Bhūmi or the earth is considered as a ‘loka,’ a place for doing karma or actions and enjoy their fruits. Hence, it is this earth with all its living beings, that has been designated as ‘bhūloka.’ It is the first of the three lokas, the other two—higher ones—being bhuvarloka (the mid-region) and svarloka (the heaven). Sometimes, the lokas are enumerated as fourteen, in which case bhūloka is described as situated in the middle, with six lokas above it and seven below.
The surface of this bhūloka is in the form of a lotus leaf, consisting of seven dvīpas (continents or islands) arranged in the form of concentric circles round the central land mass called the Jambūdvīpa. The other dvīpas are: Plakṣa, Śālmala, Kuśa, Krauñca, Śāka and Puṣkara. All these are surrounded by oceans containing different kinds of liquids like water, milk, curds or cane juice.
Of these dvīpas, the Jambūdvīpa is considered as more relevant to us since the Bhāratavarṣa (the Indian land mass) is situated in it.
For details see Bhāgavata (5.16-19).