Quoting John Lamb
Antialiasing is a technique whereby the pixels on the edge of a curve are given a shade intermediate between foreground and background. So, if a letter O is drawn antialiased black on white, the curved edges will have pixels in various shades of grey. If it works well, you get a letter O that looks more realistic. It requires quite a bit more processing to draw letters and is more useful if you have a large or low resolution monitor monitor screen.
Your application is probably a Gtk app that uses pango. Check /usr/share/doc/pango for more information. SuSE 9.0 probably uses both pango and xft2.
KDE has a feature for turning font antialiasing on and off in the control center and I think it's now on by default. I don't know whether this makes any difference to Gtk apps.