In
mathematics, a
rate is the
ratio between two related
quantities Often it is a
rate of change. If the unit or quantity in respect of which something is changing is not specified, usually the rate is
per unit of time. However, a rate of change can be specified per unit of
time, or per unit of
length or
mass or another quantity. The most common type of rate is "per unit of time", such as
speed,
heart rate and
flux. Ratios that have a non-time denominator include
exchange rates,
literacy rates and
electric field (in volts/meter).