CTR, known also as Click Through Rate, is the rate of users clicking through your listing in a Search Engine to your landing page.
Ranking is the average position your website has in any given Search result in a Search Engine.
Impressions are the number of users who had eyeballs on your website listing in a search result.
Clicks are the number of users who actively clicked on your website listing in a search result.
Metadata is the Page Title and Description your web page displays in a search result.
Search Terms are terms a user will enter in a Search Engine to find what they are looking for.
Variations are often more than one set of Metadata copy (Page Title and description) used to test a specific or multiple search results to improve overall rankings, impressions, and clicks.