What is a conversion factor?
a derived unit with a new name
the graph of recorded data
the density of a substance
a ratio of equivalent units

A ratio of equivalent units

Explanation:

A conversion factor is a ratio of equivalent units and depends on which units are to be converted.

For example we want to convert 275 [mm] to inches, so we have to find the right conversion factor to allow us to work that conversion.

275 [mm] = inches = ?

In this case the ratio is 1/25.4 = 0.039 [in/mm]

from

explanation:

wind is defined by the direction it blows from.   for example, a wind blowing from north to south is called a northerly wind.