From eta's link:
Eurasia refers to the combined land mass of Europe and Asia. Eurasia is alternatively considered to be a continent, or a supercontinent composed of the continents of Europe and Asia.

Due to the cultural differences between Asia and Europe, the historical tradition is to consider them separate continents. (This is controversial, as many historians perceive much of South and West Asia as historically closer to Europe than to East Asia). The earth sciences, with a more precise definition of continent, more frequently consider Eurasia to be a continent in and of itself.