Kahului is the city where you will likely fly in and out of the airport. There are some nice amenities here, like Costco and Whole Foods, but the truth is, you will most likely leave here as quickly as you can to head to the resorts. This is not the destination in Maui, but it is a great resource if you need it.
Kahului is "town" to locals. Office max, old navy, sports authority and other non-tourist shops and restaurants.