When you go in order of turns that's the order. It also represents one's turn in said order as well.
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.
Koichi replies to his emails in order.
I'm waiting for my turn to pay at the grocery store at the moment.
Don't push and wait your turn, please!