its Nominative form is "присваивание". It is a deverbal noun for the verb присваивать "to appropriate" (you can clearly see the connection to the word "свой" here). Well, the verb can actually have two meanings -1. to take for your own or 2. to assign some rank to a person/ value to a variable/ name and so on. Thus, the noun also has these two meanings - an act of assignment or an act of taking ownership and possession over something.
Not a very useful word but it does have a meaning.