A Rate

(obsolete) The worth of something; value. [15th-19th centuries]
The proportional relationship between one amount, value etc. and another. [from the 15th century]
Speed. [from the 17th century]
The relative speed of change or progress. [from the 18th century]
The price of (an individual) thing; cost. [from the 16th century]
A set price or charge for all examples of a given case, commodity, service etc. [from the 16th century]
A wage calculated in relation to a unit of time.
Any of various taxes, especially those levied by a local authority. [from the 17th century]
(nautical) A class into which ships were assigned based on condition, size etc.; by extension, rank.
(obsolete) Established portion or measure; fixed allowance; ration.
(obsolete) Order; arrangement.
(obsolete) Ratification; approval.
(horology) The gain or loss of a timepiece in a unit of time.

Calculus

Related Rates: (koblede rater)

Related rates is a calculus concept that describes how the speed of one changing quantity is mathematically linked to the speed of another changing quantity.

Whenever two physical things are connected to each other, the speeds at which they change over time are also connected. Knowing how fast one thing is changing, a related rates calculation leads figuring out exactly how fast the other thing must be changing.

A conceptual example: blowing up a spherical balloon.

Pumping air into a balloon at a steady speed (a constant rate of change in volume).
As the balloon gets bigger, its radius also grows.
However, the radius doesn't grow at a steady speed. When the balloon is small, the radius grows very quickly. When the balloon is already huge, that exact same amount of air barely makes the radius budge.