Harai Goshi (sweeping hip) is the throw of the week(s) for the regular adult classes and kids intermediate/advanced. This is big forward throw that is very fun when you hit it right. It falls in to the category of Koshi Waza, or hip throws. It is closely related to O Goshi (big hip throw aka the mother of all hip throws).
Just like any throw, there are many different ways to do Harai Goshi. Learn the basics and then find what variation works for you!