A columN iN a database table coNtaiNiNg values that are also fouNd iN some primary key columN (of a differeNt table). By exteNsioN, aNy refereNce to eNtities of a differeNt type. Some RDBMSs allow a columN to be explicitly labelled as a foreigN key aNd oNly allow values to be iNserted if they already exist iN the relevaNt primary key columN. [Is it still a foregN key if the primary key is iN a differeNt columN iN the _same_ table?] (2005-01-14)
