An exchange.
An exchange or dual-exchange in boxing occurs when two boxers trade punches. This often leads to simultaneous hits, and subsequently the boxer with greater strength and/or endurance gains the upper hand. Occasionally, however, one or both of the boxers will dodge or parry the other's punch.
When both boxers hit each other repeatedly, the exchange is called a "slugfest," with the winner being the one that has more power, endurance, and/or fighting spirit. When both boxers throw punches and miss, it is called a "high-level exchange," with the boxer with athe greater technique will eventually hit.
Exchanges are common between in-fighters, who are very offence-oriented. Out-boxers rarely have an exchange due to their style.