What is the distance for calculating speed?

Answer 1

Speed is a combination of the distance travelled in a given amount of time.
You can use any unit of distance and any unit of time. Choosing the units most applicable to the situation.
Most people are familiar with the units miles or kilometres per hour. Feet or metres per second.
Light speed is usually measured in kilometres or miles per second.
The growth of a stalagmite may be measured in inches per century

Answer 2

The displacement over a unit of time - which is usually a second or an hour.

Answer 3

The relationship between distance and speed is as follows:distance = speed x time