What term describes something that is easily understood and clear?

The term that describes something that is easily understood and clear is "lucid." When a concept, explanation, or piece of writing is described as lucid, it means that it is expressed clearly and comprehensibly, allowing the audience to grasp the ideas without difficulty. This clarity is essential in effective communication, ensuring that the intended message is conveyed without misunderstandings.

In contrast, terms like "confusing," "opaque," and "ambiguous" reflect a lack of clarity. These words suggest that the information might be difficult to decipher, understand, or interpret, which stands in contradiction to the characteristics of being clear and easily understood. Thus, "lucid" is the term that best fits the description required by the question.