Pentecostal Christians are Protestant Christians who believe the baptism of the Holy Spirit in Acts 2 on the day of Pentecost is an experience today for followers of Jesus. Pentecostals derive their name from this event—the day of Pentecost.
Pentecostalism is a Christian denomination, or movement, with a worldwide participation of upwards of 700,000,000 million people. Pentecostals believe the experience of the baptism of the Holy Spirit is a separate event from that of the salvation, or getting saved, experience. While that particular instance, receiving the Holy Spirit baptism at the moment of salvation, occurred in Acts 10 with Cornelius and his household, it seems to be an exception. Pentecostals believe that a sign of the baptism of the Holy Sprit is speaking in tongues. They believe that the speaking in tongues is the physical evidence of having received the Holy Spirit baptism, and should happen immediately. Among the more popular Pentecostal Churches are the Assemblies of God.
Some of the beliefs of the Pentecostal movement: the baptism of the Holy Spirit; divine healing; and speaking in tongues, spilled over into other Protestant, Catholic, and Orthodox churches. This was the beginning of the Charismatic Movement.