IF a condition is true, do something, ELSE (otherwise) IF another condition is true, do something, ELSE do this when all else fails. Note that there is no else if construct specifically, just if and else, but the syntax allows you to place else and if together, and the convention is not to nest them deeper when you do. For example: More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.