Federicis sign, also known as the "sign of the letter F", is a neurological phenomenon that has various synonyms. Commonly referred to as "reversed Phalen's sign", it describes a finger flexion test used to assess carpal tunnel syndrome (CTS). It denotes a positive result when the index finger is unable to flex effectively due to compression of the median nerve in the wrist. Alternative terms that can be used interchangeably with Federicis sign include "reversed Phalen's test", "abnormal Phalen's sign" or "negative Phalen's sign". These synonyms help medical professionals communicate effectively about this diagnostic sign and its implications in CTS evaluation.