Balanced

Balanced is a commonly used term that could have two meanings:

A balanced party
A balanced party will include:
 * 2-3 frontliners (usually Warriors or Dervishes)
 * 2-3 midliners (Mesmers, Elementalists, Necromancers)
 * 2 backliners (Monks and other healers)
 * 1 support (Runners for GvG)

A balanced skill
A balanced skill is a skill that is powerful enough it warrants usage, but not so overpowered that it is being used more than skills that are alike. A good example is Diversion. It's a very powerful skill when seen at first, but the fact that it only lasts 6 seconds is what makes this skill balanced.