Contrary to the other definitions of the word on this site, froob acually stands for frugal-noob (fr-oob). It is most commonly seen in the MMORPG Runescape
where trading is a huge part of the game. It refers to a player who has little game money in accordance with his/her combat level. Players who concentrate their efforts on combat skills only, end up having a high combat level, but do not have the non-combat-skills or understanding required to make money.
Froobs can usually be identified by comparing a player's combat level with the armor or other garments he/she is wearing. To make certain, one can look up that player's levels. High combat levels and nothing else means the player is either a froob or a type of combat pure.
In another case, froob can apply to any player who is unwilling to spend money for something he/she needs unless the trade is greatly in his/her favor.
Froobs often end up becomming pkers. Froobs pkers generally look for lower levels to kill because they do not have the weapons or ability to fight higher level pkers.
They also resort to begging for items or money.
"How sad... there is a level 113 who can't afford full rune."
"When I bought full dragon when it was 21mil, I had a combat level of 74, making me an anti-froob"