Realism: The belief that there are real entities that exist independently of human knowers. There are many types of realism, depending on the scope of the theory and the contrasting antirealist position. [...] Realism (and its rival antirealism) can also be restricted to particular regions. Thus one can be a realist (or antirealist) about unobservable scientific entities such as quarks or abstract logical entities such as sets and numbers.1
1. C.Stephen Evans, Pocket Dictionary of Apologetics & Philosophy of Religion (Downers Grove, IL: InterVarsity Press, 2002), p. 99.