I've never seen these characters before and never seen them in action either.
Does anybody know what they are and what they're used for?
Maybe somebody has this drop of trivia lying around...
These are U+fb01 and fb02, Latin Small Ligature Fl and Fi. They are in Unicode really only because they were contained in legacy 8 bit character sets like MacRoman, but should no longer be used for anything. In modern technology such ligatures are created by fonts on the basis of the underlying codes for the separate characters, which is what should aways be input in place of option shift 5/6.
They are called ligatures and they are from the days of metal typesetting. 2 letters that commonly occurred together would be forged as one piece of metal type. Nowadays on the computer, they are sometimes included in fonts, in order to make a more pleasing letter group. They are not special characters, really it is just supposed to be letters f and i drawn together.
The search tern to use is ligature
ﬂ and ﬁ are ligatures i.e. the two characters are joined together as one thing (Wikipedia says glyph). This is just how typesetters think make the text look better so is a design idea makes ﬂ look better that fl and ﬁ better than fi
The only thing I have seemed them used for explicitly is the abbreviation for florin ﬂ which used to be the Dutch currency.
They are U+FB02 LATIN SMALL LIGATURE FL and U+FB01 LATIN SMALL LIGATURE FI, which are ligatures encoded as separate characters. According the Unicode FAQ on ligatures, they “exist basically for compatibility and round-tripping with non-Unicode character sets” and “Their use is discouraged.” However, in many contexts, they are the only way to get such ligatures.
Advanced rendering software may be able to map character pairs like “fi” and “fl”, written using normal Ascii characters, to ligature glyphs, usually depending on software settings. However, most text editors and word processors cannot handle that.
Depending on font, you might have good reasons for using ligatures. In some fonts, e.g. an “fi” combination looks bad (maybe with the “f” almost hitting the dot of “i”), unless a ligature is used.
Yet, keyboard shortcuts for the ligature characters are not very useful. If you decide to use such characters, it is usually better to type the text normally, then run a global replace where e.g. “fi” and “fl” (and maybe “ffi” and “ffl”) are changed to ligature characters.