There are two terms, rather close: присваивание and присвоение. They have mainly the same set of meanings (the difference is often contextual and relates to the big and complicated topic of verb aspect) but as a matter of fact the former is used mainly in programming while the latter - as a legal or military term.

In programming:
Операция присваивания - assignment operator.

As legal term:
appropriation of a piece of property [of the best land] — присвоение (чужой) собственности [лучшей земли]

As a military term:
promotion by merit — внеочередное присвоение звания