A Barrier spell is a protective spell in multiple Schools of Magic, available to any spell caster who has attained at least a 1st level of training in a relevant School. Barrier spells are Persistent Spells.
Most Barriers have stronger forms known as Greater Barriers. Greater Barriers usually have additional effects woven into the spell-work and often require expertise in your chosen School. Greater Barriers can be strengthened further into Shield spells, further refining the spell-work into the strongest and most complex form and usually requiring a mastery over your School of study.
Mana is woven into a magical barrier that forms around you in a roughly ovoid shape, large enough to cover your entire body. The barrier is translucent and made of the type of energy of the School from which it was cast. The energy of the barrier gives off light (see individual spells for details.)
The barrier is only solid when the caster wills it to be, and solidifying a barrier allows a spell caster to defend themselves with the power of their mind, rather then physical strength or dexterity.
Damage sustained when defending in this manner is dealt first to the barrier itself, which has strength depending on the mana spent. When the barrier's strength is depleted it fades, and any excess damage is dealt to the caster.