Guaranteed inventory is a term used in the context of online advertising to refer to the practice of selling ad impressions on a website or app in advance, at a fixed price. Guaranteed inventory allows advertisers to purchase a certain amount of ad impressions on a website or app, and to know in advance exactly how many impressions they will receive and at what price. Guaranteed inventory is often used by advertisers to ensure that their ads will be shown to a specific audience, at a specific time, and at a specific price. Guaranteed inventory can also be beneficial for publishers, as it can help them to monetize their inventory more effectively and to attract high-quality advertisers. However, guaranteed inventory can also be inflexible and may not always provide the best value for advertisers or publishers.