Abjurations are protective spells. They create physical or magical barriers, negate magical or physical abilities, harm trespassers, or even banish the subject of the spell to another plane of existence.
For a list of all spells which are of the school of Abjuration, see: Category:Abjuration spells.
Abjuration is never able to be chosen as an opposition school by any wizard meaning these spells are always available to all wizards. This means there is little need to discuss the pros and cons of the entire school in case you could choose to have it as an opposition school. Abjuration's opposition school is Conjuration.
All round, this school is geared towards magical battles and the removal or protection against magic.
Because of a distinct lack of barriers from the school of Abjurations, the rules regarding casting them near each other, and other rules relating specifically to Abjurations don't apply to NWN2.
In addition, because of the lack of barrier spells, many alternative new spells like Spell Mantle were created to fill the Abjuration spellbook.