Final answer:
A testable explanation for an event in scientific inquiry is known as a hypothesis, which is a crucial early step in the scientific method and differs from a theory, which is a broad and well-supported explanation.
Step-by-step explanation:
A suggested and testable explanation for an event is called a hypothesis. This fits within the scientific method as a preliminary step before conducting experimental research. A hypothesis is a tentative explanation that can be tested by further investigation or experimentation. In contrast, a theory is a well-substantiated explanation of an aspect of the natural world, which is supported by a significant body of evidence and is much stronger than a hypothesis. Finally, a controlled experiment is an experimental design where all variables are held constant except for the one being tested, ensuring that the outcome of the experiment is due to the manipulation of the independent variable alone.