This Triad provides the foundation for semiotic research. We could call anything at all 'cat'. One signifier can have multiple signifieds. Each of these signifieds may themselves become signifiers, and so forth. The referent is in the world.
Cultural groups have to agree on what a cat is.
Signs and Systems' Tools for Cultural Studies in Book of Readings To Recap. The sign consists of the signifier and the signified. The signified is the abstract concept. Together the signifier and the signified make up 'the sign'. Signs do not have a single meaning, but many meanings.