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.
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.
The conspiracies came together on 9 Thermidor (July 27) when members of the national bodies of the revolutionary government arrested Robespierre, as well as arresting the leaders of the Paris city government.
The prime mover, however, for the events of 9 Thermidor was a Montagnard conspiracy, led by Jean Lambert Tallien and Bourdon de l'Oise, which was gradually coalescing, and was to come to pass at the time when the Montagnards had finally swayed the deputies of the Right over to their side.
On 9 Thermidor, in the Hall of Liberty in Paris, Saint-Just was impugned by Tallien whilst he was reading a report to the Committee of Public Safety, and who then went on to denounce the tyranny of Robespierre.