Wikipedia
rxvt-unicode, commonly known as urxvt, is a color VT102 terminal emulator for the X Window System. It was written by Marc Lehmann, who forked it from rxvt in November 2003. Stability, internationalization, the capability to display different fonts and locales simultaneously and support for Unicode are its primary focuses.
Another goal of the project is to be resource-friendly like rxvt. Even though it has features such as transparency, Perl extensions, and support for Xft fonts, it can still be configured to be lean and efficient, according to the author. Furthermore, it has a daemon mode that reduces memory usage and loading time when using multiple terminals.
After aterm was merged into rxvt-unicode, it is now the preferred terminal emulator for the AfterStep window manager.