What is the part started with `#` in a url?

In a url such as http://ift.tt/2sdpEZ7,

• what is the part started with # called?

• How is it implemented?

• Without looking for a clickable link (which can be absent, for example, in the following example), but by other ways such as reading the source of the webpage, will I be able to find out what to write after # to link to some line in a webpage?

  For example, how can I get a link directly jumping to "Changing Employers" in http://ift.tt/2sX2zqF?

Thanks.