Back in the old days, the system font on the Macintosh was Chicago. This was a simple boxy font that was used in the menus, buttons and such on the Macintosh. It was designed for readability on a monochrome monitor in 12 point - no anti-aliasing. This font remained until Mac OS 8 when it was replaced by Charcoal. Charcoal represents a break from the classic naming system of Macintosh fonts - normally named after cities related to the name of the "real" font it was designed after... One should note that these are all designed as screen fonts rather than printer fonts.

The Charcoal font family contains only one member - the Charcoal font itself. It is similar to its predecessor in being a simple font that is designed to be easy to read. Designed by David Berlow (who also developed a number other fonts and is known for low resolution type design along with the first True Type fonts).

Charcoal is a sans serif font - it has no serifs in its design (the classic example of a san serif fonts is Helvetica). Sans serif fonts are commonly used in computer applications being easier to render and not as confusing to the eye - simple lines and curves. Fonts with serifs are more often found in the print media (such as the newspaper) where the the serifs give visual hints as to the letter itself and make it easier to read at small sizes (paper costs money).

With the prevalence of True Type fonts, the lack of monochrome monitors and faster computers, Charcoal has a less boxy appearance and more graceful curves than its predecessor. This can especially be seen in the lower case 'i' and 'j' where the dots are circles rather than rectangles.

I keep saying Chicago was "boxy" - and I mean it literally, the 'A' looks more similar to an 'H' than an upside down 'V'. This was an advantage with slower computers - with simple kerning pairs. A kerning pair is definition about how much space a letter takes up. This can be seen in proportional fonts (mono-space fonts never enter into this) where the letter combination 'AV' takes up less room than 'AA' because the 'V' and the 'A' can slightly overlap. Charcoal, not being quite as boxy as Chicago was has many such kerning pairs allowing it to take up less screen space without sacrificing readability.