From AMS Glossary
In climatology, the degree to which a point on the earth's surface is in all respects subject to the influence of a landmass; the opposite of oceanicity (or oceanity).
Continentality usually refers to climate and its immediate consequences. Usually, it is measured by the range of temperature, either the daily range or the difference between the average temperatures of the warmest and coldest months. Since the latter increases with the latitude, a convenient measure is the annual range of temperature divided by the sine of the latitude. In another form, the difference between January and July mean temperatures at a station is divided by the difference between the January and July means for the whole circle of latitude. An index of continentality, or coefficient of continentality, k, has been formulated by V. Conrad as follows:
where A is the difference between the mean temperature (°C) of the warmest and coldest months and φ is the latitude of the place in question.
Conrad, V. 1946. Methods in Climatology. Harvard University Press, . 296–300.