The name has a rather unfortunate origin with the "Jim Crow laws" (named after a "minstrel" character) that enforced segregation in the southern USA after the Civil War. Though they were designed to prevent newly freed slaves from voting, the laws couldn't be written to flat-out say, "Black people can't vote." So state legislatures enacted "poll taxes" (not a poll tax in the traditional sense of a fixed quantity everyone pays each year,note but a literal one: If you go to the polls and can't pay, you can't vote), which disqualified most black votes because they were poor, and "literacy tests," which disqualified black voters, because they were illiterate. Not that literacy would have helped them, since these "tests" were also arbitrarily difficult (with questions like "name all the county judges in the state," or "name the exact date Oklahoma was admitted to the Union," or "how many bubbles are there in a bar of soap?") and had completely subjective scoring: White guy takes the test and gets 5/10? Passes. Black guy takes the test and gets 10/10? Make him take it again. In French. However, many white farmers were also poor and illiterate, meaning the Jim Crow laws would have affected them as well. In response, the legislatures changed the laws to, effectively, guarantee that anyone whose grandfather had been able to vote—or would have been able to vote, had he lived in the state—could himself vote without paying the tax or proving literacy. As the grandfathers of most black farmers were slaves and thus unable to vote, while almost all the grandfathers of white farmers were citizens and able to vote, this served as an effective measure for disenfranchising African-Americans without hurting poor whites. However, sometimes the laws were worded in such a way as to also discriminate against poor whites, especially in places and times when they were hostile to the local democratic party. At some times more whites were disenfranchised than blakcs by laws ostensibly targeted at African-Americans. These kinds of grandfather clauses were found unconstitutional in 1915; the rigged tests and taxes stayed until the Civil Rights Movement. In more recent times, a grandfather clause can come into effect when any sort of laws are altered or updated, so that existing buildings, tenants or procedures are not affected. For example, when a realty company changes their regulations regarding pets, it's common to allow anyone who already had one to keep them, and simply disallow new pets.