Final answer:
Pentecost is the event where the Holy Spirit gave the Church power to fulfill Jesus' mission. It is commemorated fifty days after Easter and is described in Acts 2.
Step-by-step explanation:
Pentecost is the event in which the Holy Spirit descended upon the Apostles, granting them power to fulfill Jesus' mission. It is commemorated fifty days after Pascha (Easter) and is described in Acts 2. The Holy Spirit appeared as tongues of fire and enabled the Apostles to preach in different languages.