Dear Student,
A guillotine is a device with two poles and a blade in the middle. The person's head (who is to be beheaded) is placed in the middle of the poles and the blade is then dropped on his/her head. The device was named after Dr Guillotin who invented it.
It was most popularly used during the Reign of Terror (1793-1794) in France when many people were beheaded using the killing machine. Though designed as a mechanism to curb the 'enemies' of the French Republic, even Louis XVI, Marie Antoinette and Maximilian Robespierre were guillotined.
Regards