Final answer:
The term 'theory' in a science textbook signifies a well-substantiated explanation based on extensive evidence, not merely an educated guess, making the statement true.
Step-by-step explanation:
The statement 'A science textbook uses the word "theory" to describe an idea, because scientists are very confident that the idea is correct based on lots of observational evidence supporting the idea' is true. In the scientific community, the term "theory" refers to a well-supported, thoroughly tested explanation for a set of natural observations. It is not a random or uneducated guess, but a substantial and often unchanging concept that has withstood rigorous testing through observation and experimentation.
For instance, the theory of evolution, the atomic theory of matter, and the germ theory of disease are not simply educated guesses; they are established principles supported by a multitude of experimental evidence. A scientific theory is more akin to a fact than a guess, due to the extensive support it has received from the scientific community.
Therefore, when a science textbook refers to a 'theory,' it implies a high level of confidence in the explanation's accuracy, backed by a significant body of evidence and scientific consensus.