A favorite son (or a favorite daughter) is a political term.
At the quadrennial American national political party conventions, a state delegation sometimes nominates and votes for a candidate from the state, or less often from the state's region, who is not a viable candidate. The technique allows state leaders to negotiate with leading candidates in exchange for the delegation's support. The technique was widely used in the 19th and early 20th centuries. Since nationwide campaigns by candidates and binding primary elections have replaced brokered conventions, the technique has fallen out of use.
A politician whose electoral appeal derives from his or her native state, rather than his or her political views is called a "favorite son." For example, in the United States, a presidential candidate will usually win the support of his or her home state(s).