""I suspect we are forcing the Humans into a tighter arena than they care to fight in - soon we may be able to use the Sharquoi.""
— A cryptic mention of the Sharquoi

The Sharquoi is a Covenant-related entity. Near the end of the Human-Covenant War, around the time of the Battle of Earth, a Sangheili expressed to one of his comrades that they may soon deploy the Sharquoi.[1]

Identity

"Q: What's a Sharquoi?"
— Fizzguy47

"A: Very freaking dangerous."
Frank O'Connor[2]

It is unclear to what the term Sharquoi refers, except that it is very dangerous. If the conversation is set during the Battle of Mombasa, Sharquoi may be the Sangheili name for the Scarab. Another possibility is that, (via retcon), Sharquoi is the proper name of the Kig-Yar Skirmishers; as their numbers were severely dwindled during the Fall of Reach, it is likely that the Covenant would limit their subsequent deployment until a significant advantage was held.

Sources