Spigeliuss line, also known as the semilunar line, is an anatomical reference point used in medicine and surgery. This imaginary line is named after Adriaan van den Spieghel, a 16th-century anatomist. It demarcates the transition from the three lateral abdominal muscles with the rectus abdominis muscle. While commonly referred to as Spigeliuss line, it is important to note that it is also referred to as the semilunar line due to its curved shape resembling a crescent. Synonyms for this anatomical landmark include Spiegel's line, Spieghelian line, linea semicircularis, and linea semilunaris. Professionals in the medical field often use these terms interchangeably when discussing the abdominal wall anatomy.