What is the term for a testable explanation in the scientific method?

The term for a testable explanation in the scientific method is a hypothesis.

A hypothesis is a provisional explanation proposed to account for observations or answer a scientific question. Its defining feature is that it leads to predictions that can be investigated through observation or experiment. A useful hypothesis must therefore be testable, and it should generally be possible for evidence to show that the prediction is false; this quality is often described as falsifiability.

A hypothesis is not the same as a fact, which is an observation or established piece of evidence. It is also different from a scientific law, which describes a consistent pattern in nature, and from a theory, which is a broad, well-supported explanatory framework. A hypothesis may be supported by repeated evidence, revised, or rejected; it does not become a theory simply because it survives one experiment.

For example, a researcher might hypothesize that increasing light exposure will increase a plant’s growth rate. The researcher can then control other variables, measure growth, and compare the results with the prediction. Scientific investigations are not always perfectly linear, but hypotheses make questions precise enough to test.