Most Pentecostals don't even understand everything about Pentecost.
All they understand is the Pentecost of Acts. And then they cling to speaking in tongues. Some denominations, such as AoG, won't allow you to hold office without evidence Baptism of the Holy Spirit, with the initial evidence of speaking in tongues. I should know, I was raised AoG. AoG doesn't believe you've received the Holy Spirit without speaking in tongues.
Very few Christians understand that Pentecost was celebrated by the Jews for thousands of years before Jesus. Judaism calls Pentecost "Shavuot", and it is one of the Feasts of the Lord in Lev. 23.
Pentecost is actually derived from Pente, which means 50.
Pentacost is celebrated fifty days after Easter (The feast of First Fruits).
SHHH.... Don't tell the Christians that they're celebrating one of the Lord's Feasts, by celebrating Pentecost. They may decide that they've come under the Law.
Jews celebrate Shavuot as the first time Moses received the Law and came down from the mountain. 3000 people were killed that day because they were worshiping the golden calf. Interestingly enough, 3000 people were saved on the first Pentecost after Christ's resurrection.
This is a beautiful illustration of how observing the Letter of the Law brings death, but observing the Spirit of the Law brings Eternal Life.