Which term refers to something that is free from error and conforms exactly to truth?

The term that refers to something that is free from error and conforms exactly to truth is "accurate." Accuracy implies a degree of precision that indicates the correctness of a measurement or statement in relation to a true value or standard. In various fields, especially in surveying and data collection, accuracy is critical as it ensures that the results reflect reality without discrepancies.

In contrast, "appropriate" relates to suitability or fitness for a particular purpose, but it doesn't imply correctness or truthfulness. "Valid" pertains to the soundness or cogency of an argument or measurement but might not necessarily reflect accuracy in the context of truth. "Reliable" deals with the consistency of a measurement over time or across different scenarios; something can be reliable yet not accurate if it consistently yields the same incorrect results.

Thus, in the context of something being completely free from error and aligning perfectly with truth, accuracy is the most fitting term.