https://en.wikipedia.org/wiki/Typographic_ligature
When I learned how to set lead type, we had a tray with letters for "fi", "fl", "ffi", "ffl", and some other combinations. They looked like this:

Unicode has ligatures too:
https://en.wikipedia.org/wiki/Typograph ... alphabets)
fi = fi
fl = fl
Unicode also supports the Greek Ȣ ligature for ου.