In the context of Joel, to prophesy is to proclaim truth from God, to see visions is to have a revelatory experience whilst you are awake,1 and to dream dreams is to have a revelatory experience whilst you are asleep. In each case there is revelation from God that is shared or given to someone who then shares it with someone else. In the context of Peter’s speech, to prophesy is to proclaim the mighty acts of God (Acts 2:11).2 It appears as if Peter considers the foreign languages that have come from the Spirit to be a fulfillment of the prophesy, dreams, and visions to which Joel looked forward.3
17 “‘And in the last days it shall be, God declares, that I will pour out my Spirit on all flesh, and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams;