An open-source bounty is a monetary reward for completing a task in an open-source software project.
Bounties are usually offered as an incentive for fixing software bugs or implementing minor features. Bounty driven development is one of the Business models for open-source software. The compensation offered for an open-source bounty is usually small.
When open-source projects require bigger funds they usually apply for grants or, most recently, launch crowdsourcing or crowdfunding campaigns, typically organized over platforms like Kickstarter or BountyC (since 2004 also crowdfunding).