Furikawari is a Japanese go term meaning an exchange of potential territories. It is frequently used to describe situations where potential territory is exchanged for influence or two territories are exchanged, and usually involves sacrifices. In English, the term is often translated, simply, as exchange.
Furikawari can occur from strategic sacrifices and various tactical reasons, such as kikashi moves and ladder breakers ignored. A ko furikawari occurs when one player ignores a ko threat to win a ko.
Many types of furikawari can occur in real games. For example, a player may sacrifice territory on the side to gain territory in the opponent's corner. In another example, a player invading a large framework may live inside, but at the cost of the opponent building-up large influence. Thus, a furikawari may occur between two territories, between two influences, or between territory and influence.
The key to successfully using furikawari is to use them to maintain territorial and influential balance. Flexible thinking is a must in Go.
Example 1: Strategic sacrifice
After at a the exchange of for a deep framework comprising the whole top left is complete.
Example 2: Corner vs Outside
...cutting off the stones on the top side.
Example 3: Kikashi move ignored
Because he was worrying about this line. White's left side is larger and the vital stones are not yet captured. In this line, the preliminary exchange of and helps White. On the other hand, has limited effect to the already strong White's upper left corner.
Example 4: Successive exchanges
A huge furikawari was seen in Sakata (7p, White) against Takagawa (7p, Black) in the 1952 Honinbo Challenger Playoff. Takagawa, the underdog in this game, allowed a huge right-side moyo to be killed, in return for taking the left side. He was about 20 points ahead when Sakata resigned. This brilliant game enabled Takagawa to challenge for the Honinbo title, the start of his famous series of nine wins in a row.
 Or make an approach move in an approach ko.  From Now I Would Play This Way?, p. 34.