Pearly gates is an informal name for the gateway to Heaven according to some Christian denominations. It is inspired by the description of the New Jerusalem in Revelation 21:21: "The twelve gates were twelve pearls, each gate being made from a single pearl."

Why do they call them the pearly gates?

The name for the Pearly Gates Playground is derived from Christian tradition as the entranceway through which souls travel to reach their god after death. The gates of heaven are said to be guarded by Saint Peter, one of the founders of the Christian Church.

What pearly means?

1 : resembling, containing, or adorned with pearls or mother-of-pearl. 2 : highly precious.