The point of this post is not to explain the technicalities and details of Markdown, but to underline why its use is a benefit.
Markdown is a syntax to write plain text which can be formatted in a really simple way and in any text editor—even in the notes app of your phone.
As its creator defines it, Markdown is two things: (1) a plain text formatting syntax; and (2) a software tool, written in Perl, that converts the plain text formatting to HTML. Even though it was initially intended for conversion to HTML, there are many other possible uses due to its flexibility.
Markdown simplifies the act of writing—reducing the text-formatting possibilities of your writing to essential markup. This way, you can not get lost in formatting tools, and can completely focus on your content.
As the syntax is widely used, more and more tools are being released in order to make Markdown compatible with almost everything—it is supported by WordPress, for instance. It can be used to post, create rich-text documents, electronic books, and a large etcetera.
In June 2014, I shared some of my Markdown Workflows to use text written using the Markdown syntax in many different environments—including Adobe InDesign, websites with Laravel, or iOS apps with Objective-C.
Markdown was created by John Gruber in 2004. You can go through its syntax and philosophy here.
If you wanna try using Markdown, you can try with iA Writer in your iOS or OS X device (it will soon be available for Android devices), with Markdrop on Android, with MarkdownPad on Windows, and with MarkdownItOnline.