Yes, you are able to place items on backorder. If an item is out of stock but will be back in stock you have the option to place them on backorder, so customers know they can still place an order for them.
In order to place a product on backorder please log into your account and on the left hand side there will be a gray column with several options. One of those options is Products. Click on this option and you will be brought to all products you have added. Once you find the product you want to place on backorder, toggle over the product and you will see several options appear. One of those options is edit. Click on this option and you will be brought into the section where you can edit this product. If you scroll down to the bottom of the page you will see a section labeled Inventory. Within in this section there is an option for stock status. If you click on the drop down you will see one of the options is On Backorder. Choose this option and make sure to click Save product.