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.
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).
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.