Well that’s what the dictionary defines as a ligature. I know the term for a very different use and if you’ve never heard of the term before, to a type designer they are a key part of building a typeface.
When certain letters are sat next to each other they can often sit uncomfortably and overlap or merge in the wrong place. Especially with serif typefaces. A really good example of this is the f and i together, where the hook of the f clashes with the of the i, just like this:
Luckily type designers who respect their art create specifically designed characters for these letter pairings and those are ligatures.
Not all graphic or web designers use them and some design programmes don’t give you the option to allow the use of ligatures. Luckily the Adobe suite does.
Since 2012, after decided to go back into web designer after a break of ten years, everything with code had changed and ligatures could now be used within most browsers and with any typeface where the typographer has created them. So i’ve been using this in all my builds since then with some very elegant results.
-moz-font-feature-settings:"liga=1, dlig=1"; -moz-font-feature-settings:"liga", "dlig"; -ms-font-feature-settings:"liga", "dlig"; -o-font-feature-settings:"liga", "dlig"; -webkit-font-feature-settings:"liga", "dlig"; font-feature-settings:"liga", "dlig";