Continents are large, continuous, discrete land-masses.
How many continents are there on Earth?
It depends on how »large«, »continuous«, and »discrete« are defined.
The answer could be anywhere from seven down to four.
In the traditional seven-continent model, the continents are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
In six-continent and five-continent models, the land masses of Asia-Europe (Eurasia) and/or North-America-South-America (America) are combined.
In the four-continent model, Africa is combined with Asia-Europe to create Afro-Eurasia.
Afro-Eurasia, America, Antarctica, and Australia. Think what a different world view that list might encourage.