For more information about “store categories” visit: Store Categories
You can organize your listings using up to 300 store categories. Your Store category total includes the sum of all level 1, level 2, and level 3 categories.
For example, you could have 300 level 1 categories or 30 level 1 categories with 10 subcategories each.
Please note: eBay automatically creates a default level 1 category named “Other Items” that can’t be edited and does count toward the 300 category limit.