In the digital advertising ecosystem, a Supply-Side Platform (SSP) is a software or platform used to help publishers, such as website owners, app developers, or content creators, to manage and optimize the sale of their advertising inventory, specifically the available ad space on their apps or websites. SSPs are a crucial part of the advertising landscape.

Here’s a breakdown of what an SSP does:

1. Inventory Management: SSPs are used by publishers to organize and manage the available ad inventory. This includes ad formats such as display ads, video ads, and native ads. 
2. Ad Auctions: Publishers are able to offer their ad impressions for sale in real-time auctions via SSPs. These auctions take place in milliseconds as a user visits a website or app, and advertisers bid on the available ad slots. 
3. Ad Exchange Integration: SSPs connect with Ad Exchanges, which are platforms where advertisers and their Demand-Side Platforms (DSPs) participate in bidding for ad impressions. This real-time auction process ensures that the publisher gets the highest possible revenue for each ad impression. 
4. Ad Quality Control: SSPs include tools that allow publishers to set rules and criteria for the types of ads that can appear on their websites or apps. This allows publishers to maintain control over the quality and relevance of the ads displayed to their audience. 
5. Real-Time Reporting and Analytics: SSPs provide publishers with real-time data and analytics that allow them to monitor ad performance, revenue, and other key metrics. This data helps publishers make informed decisions about optimizing their ad inventory. 
6. Ad Yield Optimization: SSPs use algorithms and data analysis to optimize the pricing of ad impressions in real time. This helps publishers maximize their advertising revenue by selling ad inventory to the highest bidder. 

Overall, SSPs empower publishers to effectively and efficiently monetize their digital properties while offering advertisers access to a wide range of online audiences. SSPs are a crucial part of the programmatic advertising ecosystem, facilitating the buying and selling of digital ad impressions on a large scale.