In this situation, where A gives his boat to G, G becomes the owner of a boat previously owned by A. We can describe the situation as a 'transfer' of ownership from one person to another. The right that is transferred is a property right: the right of ownership of the boat.
When a person obtains a property right from a person who held it previously, we describe this situation as 'derivative' acquisition of a legal right, to distinguish it from 'original' acquisition.
The distinction is important, because different rules apply to derivative and original acquisition of property rights.
Johnson v Buttress (1936) 56 CLR 113 (see p 210) is an example of derivative acquisition. In this case, Johnson acquired ownership of a house from Buttress, who transferred his rights to her as a gift.