Republicans In Name Only or RINO are members of the Republican Party of the United States whose views are seen as being different from those of the Republican platform.
The word usually means Republicans that do not share their views. When Theodore Roosevelt and William Howard Taft both wanted to become the Republican candidate for President of the United States they accused each other of being "Republican in Name Only". When he was President Franklin Roosevelt called Republicans who supported the New Deal "Me Too Republicans" and claimed they were just promising to do what he was already doing.
In 1964, Senator Barry Goldwater refused to run for President as a moderate because "Extremism in the pursuit of justice is no vice and moderation in the service of conscience is no virtue."
The term RINO was popularized after it was widely used in protest of the election of Richard Riordan as Mayor of Los Angeles. Republicans who are accused of being RINOs don't like it when people call them that.
Recently people have also started to call conservativeDemocratsDINOs meaning Democrats in name only.