What is online shopping mall?

Think of a retail mall, what is it? A place where you walk into a large hallway and find many stores (which are all independent) you can choose to shop at the stores you like

An online mall is a website that you walk (browse) into and you will find many stores (listings) you may choose to walk (click on the link) into any of the stores listed

An online mall is also often called a shopping directory, and just like a retail mall the mall (website) itself does not sell anything, the mall (website) website is just a wide hall/passageway to get to visit other stores that happen to have rented space in this mall (website).