Explain what the grandfather clause for voting rights was

statutory or constitutional device enacted by seven Southern states between 1895 and 1910 to deny suffrage to African Americans. It provided that those who had enjoyed the right to vote prior to 1866 or 1867, and their lineal descendants, would be exempt from recently enacted educational, property, or tax requirements for voting. Because the former slaves had not been granted the franchise until the adoption of the Fifteenth Amendment in 1870, those clauses worked effectively to exclude black people from the vote but assured the franchise to many impoverished and illiterate whites.