Demarcation
The demarcation problem refers to the distinction between science and nonscience (including pseudoscience); Karl Popper called this the central question in the philosophy of science. However, no unified account of the problem has won acceptance among philosophers, and some regard the problem as unsolvable or uninteresting.
Early attempts by the logical positivists grounded science in observation while non-science was non-observational and hence meaningless. Popper argued that the central property of science is falsifiability (i.e. all scientific claims can be proven false, at least in principle, and if no such proof can be found despite sufficient effort then the claim is likely true).
Read more about this topic: Philosophy Of Science