Parents often buy their children gender-specific toys. boys get action figures that encourage active and aggressive play; while girls receive dolls and toy ovens that encourage domestic play. this is part of what process?

This is part of socialization.
Socialization is a term which refers to learning how to behave appropriately. So, these parents want their sons to have their 'expected' manly roles, which is why they are letting them play with 'boys' toys only, whereas their daughters are expected to be more feminine and therefore can only play with 'girls' toys in order to teach them how to behave appropriately in the society when they grow up.