雷同 (léi tóng) literally combines 雷 (léi, 'thunder') and 同 (tóng, 'same'). Though the character 雷 might suggest something loud or striking, in this compound it functions idiomatically — not as 'thunder-same' but as a fixed expression meaning 'identical in an unoriginal, uninspired way.' It carries a negative connotation, implying dull repetition, lack of creativity, or suspicious similarity — especially when comparing works, ideas, designs, or answers.

The term is commonly used in academic, professional, and creative contexts: for example, to criticize copied essays, formulaic product designs, or standardized test answers that appear too alike. Unlike neutral synonyms like 相同 (xiāngtóng), 雷同 implies redundancy or imitation without added value. It’s often found in formal writing and critiques, and rarely used in casual speech about everyday objects or people unless emphasizing undesirable sameness.