Objectives and key results (OKRs) is a tool to focus, align, prioritize and measure the work of an organization in order to accomplish their mission and achieve their vision.
Objectives are goals you want achieved. They are meaningful, specific, action-oriented and aspirational.
Key Results are tasks or actions that help you reach your Objectives. They are measurable, time-bound, aggressive, yet realistic. When all Key Results are met, the Objective is necessarily achieved.
Projects are your best bets to make progress. They're the things that are most likely to move the needle. They're hypotheses, and this is also why you need to avoid treating them as Key Results. Projects are a way to make progress whereas Key Results are a measure of progress.
Here's an example of an objective with KRs and Projects:
Objective: Become the best gaming platform in North America.
Key Result: Achieve 150M Monthly Active Users
Key Result: Exceed 90% User Retention
Project: Ship new version of gaming platform
Project: Deliver social gaming features
Project: Deliver high speed gaming backbone network
You can see that the projects are not results themselves, but the work the company needs to do in order to get to the key results, or maximize their chances of achieving them. By showing key results and projects in a single view like this, an organization can have a conversation both about its strategy and the execution needed to get the strategic results.