Positivism is the view that scientific knowledge is the only legitimate or reliable form of knowledge. Other forms of justifying knowledge, such as philosophical deliberation, personal anecdote, spiritual experiences, etc, would be regarded as unreliable and hence not capable of generating genuine knowledge. Although few philosophers today would identify with this classic ‘strong’ form of positivism, various philosophers have and continue to articulate positions which are to some degree similar to, or in alignment with, various forms of positivism. The label ‘scientism’ is sometimes applied to particularly extreme forms of positivism, usually as a term of derision from those who regard such viewpoints as impoverished and overly narrow.

Further Reading

Logical empiricism: Stanford Encyclopedia of Philosophy article discusses the historical school of positivism dominant in the early twentieth century

Positivism: brief New World Encyclopedia piece outlining some of the key thinkers and views of Positivism

Positivism: an introduction to the key ideas and forms of positivism from philosophybasics.com