Complex sentence: A heptagraph is a seven-letter sequence of letters that behaves as a unit and is not the sum of its parts, such as the seven-letter German sequence, used to transliterate Russian, as in for "borscht".
Split into simpler sentences: A heptagraph is a sequence of seven letters that behaves as a unit and is not the sum of its parts. The seven-letter German sequence, used to transliterate Russian, as in for "borscht".