cn is a user attribute defined in RFC4519→ (Lightweight Directory Access Protocol (LDAP):Schema for User Applications). From RFC4519: "The cn (commonName in X.500) attribute type contains names of an object. Each name is one value of this multi-valued attribute. If the object corresponds to a person, it is typically the person's full name."
cn is commonly used to transmit a person's full name. As it is a multi-valued attribute, some IdPs may send multiple permutations of the person's name in the cn attribute.