Bonus
noun
It's a prize where you are given gold. In business, this is called a bonus. You didn't expect it (not your salary) and it is given to you (and is gold, if you're lucky).
しょうよきん
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.
給料日は毎月5日と20日で、会社の業績次第で賞与金が年末に支払われます。
Our paydays are the fifth and the twentieth of every month and a bonus may be paid at the end of the year depending on how well the company has done.