Thermidor was the eleventh month in the French Revolutionary Calendar, which was used only in France and only for thirteen years. It was the middle month of summer (being named for heat), and started on the equivalent to July 19th or 20th in the Gregorian Calendar.

Revolution of Thermidor or simply Thermidor refers to the coup of 9 Thermidor (27 July 1794) in which Maximilien Robespierre was guillotined and the Reign of Terror ended. See Thermidorian Reaction. The interval of Thermidor was followed in turn by the French Directory. Prominent figures of Thermidor include Paul François Jean Nicolas Barras and Jean Lambert Tallien.

For historians of revolutionary movements, the term Thermidor has come to mean the phase in some revolutions when the political pendulum swings back towards something resembling a pre-revolutionary state, and power slips from the hands of the original revolutionary leadership. Leon Trotsky, in his book The Revolution Betrayed, refers to the rise of Stalin and the accompanying post-revolutionary bureacracy as the "Soviet Thermidor".

The food "Lobster Thermidor" was named, directly or indirectly, after the month. (Sometimes it is said that it was first prepared for Napoleon during the month of Thermidor; others say that it was created by Tony Girod at the Cafe de Paris to celebrate the opening of a play called Thermidor.)

Lobster Thermidor was one of the last meals served on the Titanic.