A pejorative for wealthy liberals who do not want to bear the cost of the liberal policies they support. It is typically used by populists to criticize the rich members of the Democratic Party.
Examples of a limousine liberal include Democrats who champion distribution of wealth but pay their workers minimum wage, or those who claim to support environmental regulation but have a large carbon footprint.
According to Time, the term comes from the 1969 NYC Mayoral race, where it was first used by candidate Mario Procaccino to attack his wealthy opponent:
[Limousine liberals] were, according to Procaccino, who was then the city’s comptroller, insulated from any real contact with poverty, crime, and the everyday struggle to get by, living in their exclusive neighborhoods, sending their children to private prep schools, sheltering their capital gains and dividends from the tax man, and getting around town in limousines, not subway cars. Not about to change the way they lived, they wanted everybody else to change, to have their kids bused to school far from home, to shoulder the tax burden of an expanding welfare system, to watch the racial and social makeup of their neighborhoods turned upside down.