Final answer:
An initial or tentative explanation of an observation is called a hypothesis, which is a testable prediction that can be investigated through scientific methods.
Step-by-step explanation:
The initial or tentative explanation of an observation is called a hypothesis. This is essentially an educated guess based on existing knowledge that can be tested through experimentation, calculation, and comparison with other experiments. The goal is to determine whether this hypothesis can accurately predict or explain the phenomena in question. If it holds true across a wide range of observations and experiments, this hypothesis may eventually be developed into a theory, which is a comprehensive explanation for a given aspect of the natural world that is consistently supported by evidence.