The Baptism of the Holy Spirit for believers, with signs following.

Acts 1:4 through Acts 1:5 (NLT)
⁴In one of these meetings as he was eating a meal with them, he told them, “Do not leave Jerusalem until the Father sends you what he promised. Remember, I have told you about this before. ⁵John baptized with water, but in just a few days you will be baptized with the Holy Spirit.”

The baptism of the Holy Spirit is the coming of the Holy Spirit upon the believer in power for service and witnessing.

Luke 24:49 (NLT)
⁴⁹“And now I will send the Holy Spirit, just as my Father promised. But stay here in the city until the Holy Spirit comes and fills you with power from heaven.”

Acts 1:8 (NLT)
⁸But when the Holy Spirit has come upon you, you will receive power and will tell people about me everywhere—in Jerusalem, throughout Judea, in Samaria, and to the ends of the earth.”