Basic cruise control is a driver ease feature which maintains a general engine speed without the driver keeping their foot on the accelerator pedal. It does so by locking the throttle body's butterfly valve in the postion it is in when the driver presses the cruise control button.
Drive-by-Wire Cruise Control
Because the throttle body on a Drive-by-Wire vehicle is operated by an electronic actuator, the cruise control system is less complicated, only requiring the computer to stop moving the actuator.
Adaptive Cruise Control
Like the name suggests, adaptive cruise control uses various onboard sensors to adapt to changing driving conditions, usually just to deal with a slower vehicle in ahead in the same lane. The primary purpose of the system is to travel at the speed selected by the driver, the same as traditional cruise control. However, if the vehicle detects another car in front of it that is traveling at a lower speed, the vehicle will actively reduce its speed to match that of the detected car ahead and then maintain a selected buffer distance behind the car. The system works by emitting radar waves which bounce off of vehicles ahead and return to the reciever. This informs the system of the distance between the two vehicles. Changes in that distance will also be detected over time, and will be compensated for.
How Adaptive Cruise Control Works by Engineering Explained
In this video (where Engineering Explained was sponsored by Honda), Jason Fenske explains how adaptive cruise control works.
Cruise Control With Auto Braking
Vehicles designed with auto braking almost always integrate the forward object detection into the cruise control to maitain the speed of the vehicle ahead.
Cruise Control Safety
It should never be assumed that cruise control will do what you assume it will do, even with the most basic or advanced versions, so stay alert while driving and using it.