Quick Definition: Difficulty in separate science from pseudo-science or non-science
From Rational Wiki:
The demarcation problem is the philosophical problem of determining what types of hypotheses should be considered scientific and what types should be considered pseudoscientific or non-scientific. It also concerns itself with the ongoing struggle between science and religion, in particular the question about which elements of religious doctrine can and should be subjected to scientific scrutiny. This is one of the central topics of thephilosophy of science, and it has never been fully resolved. In general, though, a hypothesis must be falsifiable, parsimonious, consistent, and reproducible to be scientific.