constant
Change in speed (more precisely change in velocity) is called acceleration.
Constant speed
A change in position in a certain amount of time is called motion.
A change in speed or direction of motion is called "acceleration". If an object's speed or direction of motion changes, then the object is "accelerated".
Speed.
It is called refraction.
The change in speed of light when traveling through different mediums is known as refraction. Refraction occurs because light waves change speed as they pass from one medium to another, causing them to bend.
That is called acceleration.
Acceleration.
No, speed can vary and one can still calculate the average speed of an entire trip. Average speed is equal to the change in distance divided by the change in time.
I'm uncertain about what you are seeking here. The change in an objects speed divided by the time required to change the speed would be the average acceleration.
The speed is v and the starting speed is v0.