Protoscience refers to historical philosophical disciplines which existed prior to the development of scientific method, which allowed them to develop into science proper (see prescientific). A standard example is that of alchemy which later became chemistry, or that of astrology which later became astronomy.
By extension, "protoscience" may be used in reference to any "set of beliefs or theories that have not yet been tested adequately by the scientific method but which are otherwise consistent with existing science, [thus being] a new science working to establish itself as legitimate science".[1]
The philosopher of science Thomas Kuhn first used the word in an essay, originally published in 1970:
In any case, there are many fields — I shall call them proto-sciences — in which practice does generate testable conclusions but which nevertheless resemble philosophy and the arts rather than the established sciences in their developmental patterns. I think, for example, of fields like chemistry and electricity before the mid-eighteenth century, of the study of heredity and phylogeny before the mid-nineteenth, or of many of the social sciences today. In these fields, too, though they satisfy Sir Karl's [ Popper's] demarcation criterion, incessant criticism and continual striving for a fresh start are primary forces, and need to be. No more than in philosophy and the arts, however, do they result in clear-cut progress. I conclude, in short, that the proto-sciences, like the arts and philosophy, lack some element which, in the mature sciences, permits the more obvious forms of progress. It is not, however, anything that a methodological prescription can provide. Unlike my present critics, Lakatos at this point included, I claim no therapy to assist the transformation of a proto-science to a science, nor do I suppose anything of this sort is to be had.
– Thomas Kuhn, Criticism and the growth of knowledge[2]