A "ligature" is a character or symbol that combines two or more letters into a single shape. It is used in certain languages or writing styles to improve readability or aesthetics. Full definition
It often sounds like a foreign language when type nerds discuss the use of ligatures and descenders and the history of a typeface as seen in this example: (lawyerist.com)
Natalia Borodina Hanging is the suspension of a person by a noose or ligature around the neck. (myintimcity.com)
I love the way it looks, however I would note that whenever you use ligatures (as in the example document's first page with the ff in «Plaintiff») you run into complications. (slaw.ca)