Quick Definition: A statement that cannot be empirically tested is meaningless
From Rational Wiki:
Logical positivism is a school of philosophy that emerged out of the Vienna Circle in the early 20th century. Its proponents emphasize materialism, empiricism, philosophical naturalism and the scientific method as the highest pursuits of rational thought. The most famous principle of logical positivism is that any statement that is not inherently verifiable is meaningless and can be safely ignored. Since this statement is itself inherently unverifiable, logical positivism tells us that logical positivism can be safely ignored.
The philosophy was mostly reverse-engineered to explain the success of the scientific method. Much of ethics, theology and the supernatural is immediately reduced to nonsense under this view. Instead, it stresses skepticism, science, and reasoning grounded in an empirical reality that can be objectively perceived by all parties.
While there are some fundamental issues with logical positivism that have led to it being abandoned as a universal epistemological system, the thrust of its main argument has not been similarly dismissed. Many scientists like to talk about methodological naturalism or concepts such as NOMA as a way of allowing theological considerations to still hold some level of sway in a reality that is being increasingly defined and understood by a process that assumes the non-existence of any deity. At some point it becomes reasonable to ask: if all of our best knowledge comes from a system that assumes that there is no supernatural cause or explanation, why do we need such a cause to begin with? Positivists would hold such claims are inherently lacking in meaning and substance, and that we are better off tossing them out.