In English, Pulchritude is a noun synonymous with beauty. In MS Paint Adventures, this definition varies depending on the character. For example, it is how hard-boiled and suave a Problem Sleuth character is. A high Pulchritude stat allows the owner of said stat to influence others, get the dames, and generally be a hard-boiled fellow. Problem Sleuth, as his name is in the title, has the highest Pulchritude stat, making him the de facto leader of the team. Conversely, Ace Dick is brutish and offensive and has a low Pulchritude, although it has not stopped him from finding love on at least two occasions. (Ace Dick marries Wifehearst and fathers Bathearst; Fiesta Ace Dick fathers a child with the Demimonde Semigoddess.)
In other adventures Pulchritude pops up from time to time, but isn't significant in any manner. In Jailbreak, it is an almost useless stat that appears after the suicide/game over and your character has less Pulchritude than a pony. Embarrassing. In Bard Quest, Pulchritude is even less significant. Your character can ask the blacksmith for Bard Armor with a +5 Pulchritude bonus, but you are unable to afford it.
Pulchritude is not been mentioned in Homestuck.