Campaigns, experiments, experiences, and variations are terms related to Optimizely testing. In general, campaigns have experiences and experiments have variations. 

• Campaigns are the framework for organizing your strategy in Optimizely Web Personalization. A campaign takes some content on your site, like the promotions on your homepage, and swaps in different content for different audiences. Read about Personalization campaigns.
• Experiment is Optimizely's term for an A/B, multivariate, or multi-page test. You might also see experiments called "tests" or "campaigns." See Experiment Types: AB, Multivariate, and Multi-page.
• Experiences are the different personalized versions of your site that you create for visitors based on the page they're visiting and the audiences they qualify for. Learn more about Personalization experiences. When you are not sure what type of experience will work best for a particular audience, you can test experiences with Experimentation in Personalization campaigns.
• Variations are the alternate versions of your site that you test against your original (or baseline) in Optimizely Web Experimentation. Learn how to create and change variations in your experiments.