Final answer:
A scientific theory is a comprehensive and well-substantiated explanation that unifies observations and experiments in the natural world, such as Dalton's atomic theory which systematizes the behavior of matter.
Step-by-step explanation:
A theory in the context of science is not an unverified guess or simple speculation as it may often be used in everyday language. Rather, it is a comprehensive explanation of aspects of the natural world that is built on a body of evidence collected from numerous observations, experiments, and reasoned analysis. This scientific concept is significant because it unifies a substantial number of findings and observations under a coherent framework allowing for generalizations and predictions about new, unobserved phenomena. For instance, Dalton's atomic theory brought together a range of discoveries and laws related to the properties of matter, providing a systematic explanation of chemical reactions and the conservation of mass.
Scientific theories are well-substantiated and have been rigorously tested. They move beyond the realm of hypothesis - which is an initial, less-confirmed proposition - to reach a higher level of scientific understanding. This involves repeated experiments and observations that not only support their claims but also demonstrate a consistent pattern, reinforcing the theory's credibility and robustness.