(1) Any attribute, phenomenon or event that can have different qualitative or quantitative values. Typically, a form of metadata goes with the variable, there is a variable definition that describes what is varying and there is a value for the variable. Variables are typically assessed in a clinical trial.
When you click a link for an email address or website, your Mac opens the app you've set for that kind of link. Mail is the default email app and Safari is the default web browser on your Mac. If you install other email apps or web browsers, you might want to set them to open when you click an email link or web link. Open the Mail app.
This tutorial was last updated on March 17, 2015 and is only intended for desktop/laptop users running the Mac OS X 10.10.x (or above) operating system. While Apple's Safari is a well-known favorite among Mac users, OS X's default browser is far from the only game in town. With popular alternatives such as Chrome and Firefox available on the platform, along with other formidable options like Maxthon and Opera, it not uncommon to have several browsers installed on the same system.