Room Number, Suffix For Room Numbers
suffix
This is a counter that can be used after numbers to let you know what number room it is. It's a room number that you use in apartments and hotels to know exactly which room you're looking for.
ごうしつ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
こちらが302号室です。
This is Room 302.
今すぐホテル東京の103号室に来てもらえますか？
Can you come to Room 103 in Hotel Tokyo right now?
本社は、あのビルの507号室にあります。
The head office is located in Room 507 in that building.