A tricopter is a remote controlled aircraft. Three rotors, which generate buoyancy, are used for the movement and control. Three generally equal booms are attached on the trunk of the tricopter. The distance is 120 degrees to each other.
A multicopter or multirotor is probably what the majority of people today regard as a drone. A commonly known helicopter has one engine, while multicopters are equipped with multiple engines, one for each of the rotor arms.
The main difference between tricopters and quadcopters is that they have a different number of rotors.
Tricopters are not as popular as quadcopters, as many people overlook them because quadcopters are visually more appealing and made a huge breakthrough with their quads that made such design almost monopolistic in the industry.
The applications of tricopter are
military
filming
agriculture
search and rescue purpose