Furikawari
Furikawari, a Japanese go term, means an exchange of potential territories (which may involve quite large groups of stones changing hands, too). In English, furikawari is often translated as exchange.
A ko furikawari occurs when one player ignores a ko threat to win a ko.[1]
There are numerous types of exchange that occur in real games.
For example, one player has a large framework, which is invaded by the opponent. Whilst defending his moyo, the player builds up power (influence) which he uses to invade the opponent's territory.
The result afterwards is that the opponent may end up making territory within the original framework, whereas the framework player ends up with the territory originally claimed by his opponent. Of course this is less 'sudden', so that one can speak too of strategic exchanges, exchanges of territory for influence and the other way round.
[1] Or make an approach move in an approach ko.
See also: