To Throw Open, To Open To The Public
する verb
かいほうする
このそうこをひなん所として開放することになりました。
They decided to open this warehouse as a refuge.
このプールは、夏の間、一ぱんに開放されます。
This pool is open to the public in the summer.
あるゲームにアクセスするために、ポートを開放する方法が知りたいんだ。
I want to know how to open ports to give access to this one game.
When you open then release, say, a door, you're opening it up for everyone to come in. That's why it means to open up or to throw open.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.