Complex sentence: The case set a precedent defining "initial interest confusion"; the court affirmed a lower court's ruling that the brand Grotrian-Steinweg could cause piano buyers to confuse it with the brand Steinway & Sons.
Split into simpler sentences: The case set a precedent defining "initial interest confusion". The brand Grotrian-Steinweg was thought to cause piano buyers to have an unconscious association with the brand Steinway & Sons.