Boosting is the practice of paying to amplify an organic post so it reaches more people than it would through unprompted distribution alone. Most major platforms offer a boost button directly on published posts - you set a budget, a target audience, and a duration, and the platform serves the post as a sponsored piece of content.
Boosting sits between fully organic posting and building a complete ad campaign. It’s a quick option for increasing reach on a post that’s already performing well, but it typically offers less targeting and creative control than a dedicated ad manager campaign.