A supply-side platform (SSP) is a type of ad tech platform that is used by publishers to manage and sell their advertising inventory. It is called a "supply-side" platform because it helps publishers to manage and monetize their supply of ad space, by connecting them with advertisers and ad networks that are interested in buying that space. With a SSP, publishers are able to set the terms and conditions under which they are willing to sell their ad space, and then the SSP uses algorithms and data to match those terms with the right advertisers. This helps publishers to maximize the value of their ad inventory, and also makes it easier for advertisers to find and purchase the right ad space to reach their desired audience. In the ad tech industry, SSPs are often used in conjunction with demand-side platforms (DSPs), which help advertisers to manage and buy ad space.