A calculation is a deliberate mathematical process that transforms one or more inputs into one or more outputs or results. The term is used in a variety of senses, from the very definite calculation of using an algorithm, to the vague of calculating a strategy in a competition, or calculating the chance of a successful relationship between two people.
Statistical estimations of the likely election results from opinion polls also involve algorithmic calculations, but produces ranges of possibilities rather than exact answers.
To calculate means to determine mathematically in the case of a number or amount, or in the case of an abstract problem to deduce the answer using logic, reason or common sense. The English word derives from the Latin calculus, which originally meant a pebble (from Latin link=no), for instance the small stones used as a counters on an abacus (link=no, translit-std=ALA-LC). The abacus was an instrument used by Greeks and Romans for arithmetic calculations, preceding the slide-rule and the electronic calculator, and consisted of perforated pebbles sliding on iron bars.
Calculation is a prerequisite for computation.