Units of speed can be expressed in various ways, but they all fundamentally represent the distance traveled over a specific amount of time. Here are some common units:

Metric System:

* Meters per second (m/s): This is the standard unit of speed in the metric system.

* Kilometers per hour (km/h): Often used for road vehicles and general speed measurements.

* Centimeters per second (cm/s): Useful for describing slower speeds, often used in scientific contexts.

Imperial System:

* Feet per second (ft/s): Used in some engineering and scientific contexts.

* Miles per hour (mph): The most common speed unit in the United States.

* Knots (kt): Used for measuring speed in nautical contexts (1 knot = 1 nautical mile per hour).

Other Units:

* Mach: Represents speed relative to the speed of sound. Mach 1 is the speed of sound, Mach 2 is twice the speed of sound, and so on.

* Light-year: The distance light travels in one year, sometimes used to express the speed of very fast objects, like stars or galaxies.

The best unit to use for speed depends on the context and the scale of the speeds involved. For example, you wouldn't measure the speed of a car in meters per second, and you wouldn't measure the speed of a snail in kilometers per hour.