A soundcheck is the preparation that takes place before a concert, speech, or similar performance to adjust the sound on the venue's sound reinforcement or public address system. The performer and the audio engineers run through a small portion of the upcoming show to ensure the venue's front of house and stage monitor systems are producing clear sound, are set at the proper volume, and have the correct mix and equalization (the latter step using the mixing console). When applied to microphones exclusively, it is more commonly (and appropriately) called a mic check.
Sound checks are especially important for rock music shows and other performances that rely heavily on sound reinforcement systems.