Can a product be listed in more than one category?

Yes. If you haven’t created it yet, set up the product that you want to be listed in two or more categories. Go to the category in which you put that product, using Admin > Catalog > Categories/Products. There you will see a row of icons towards the right, one of which is a white “c” in a blue circle. Click on that and you can copy a product to another category.

There are two types of copy: linked or duplicated. In the former case the product shows in both categories but there’s only one instance, so any changes will affect both. In the latter case a new, identical product is created, which can then be changed independently of the original. This is a good shortcut for creating a new product which shares many things in common with an existing product.

Generally when you want to show a product in multiple categories, you will want a linked product (so you don’t have to maintain two different product entries). Read more about linked products.