What’s the difference between Composite Items and Kit Items?

A Composite Item is the item type that covers both sub-types: Assembly and Kit items. When creating a new composite item, you choose the Item Type:

Assembly Item - a group of items combined together to be tracked and managed as a single item. Use this when you physically build or assemble a finished product from component parts.
Kit Item - individual items sold together as one kit. Use this when you bundle separate products for sale without any physical assembly. Each component’s stock is still tracked individually.

To create a composite item, go to Items > + New dropdown > New Composite Item, select the item type, fill in the details, and use Add Product under Associate Items to add the components.