Why is Shavuot also called the Feast of Weeks? Why multiple names?

     I’m confused, why is Shavuot also called the Feast of Weeks? Why multiple names?

     Shavuot, Feast of Weeks, and Pentecost, are all names for the same Feast. All three names describe the count between the wave sheaf, occurring on the Sunday within the Feast of Unleavened Bread, and Pentecost. This count consists of seven complete weeks or 49 days, plus one additional day, making 50 days in total. In Hebrew, Shavuot mean, “weeks.” In Greek, Pentecost means, “fifty.” Both these names, along with the “Feast of Weeks,” describe this count from different perspectives.

As a side note, it’s not uncommon for Feast days to have multiple names. Below are a few examples:

The Feast of Unleavened is also called “Chag Ha-Matzot.”
The Feast of Trumpets is also called “Yom Teruah.”
The Day of Atonement is also called “Yom Kippur” or “the Fast.”
The Feast of Tabernacles is also called “Feast of Ingathering” and “Chag Ha-Sukkot”