During Grant’s presidency members of his administration took part in price skimming and tax evasion. It (the term "Grantism") also referred to how big business had begun to exert increasing control over local & national government during this time period.
The scandals that led to the term include:
The Liberal Republican faction broke off from the Republican party to oppose Grantism. In 1872 they nomminated Horace Greenley (also the Democratic candidate) to oppose Grant, but overwhelmingly lost.