Wisdom describes a character's willpower, common sense, perception, and intuition, whereas intelligence represents the ability to analyze information. An "absent-minded professor" has low wisdom and high intelligence. A simpleton with low intelligence might nevertheless be very perceptive (have high wisdom). Wisdom is important for clerics and druids, affecting the strength and number of their spells, and is also significant for paladins and rangers. It is very important for monks as well, modifying many of their abilities. The wise character is capable of intuitively understanding others, occasionally having insights into their motivations.
Classes: The classes with features affected by wisdom are those listed above, namely cleric, druid, monk, paladin, and ranger. In addition, epic shifters need a high wisdom to acquire most of their additional shapes.
The main appeal of investing in wisdom for most characters is the impact on will saving throws. This makes wisdom a less likely "dump" stat (one intentionally left as low as possible) than others, but dumping wisdom is not uncommon. By the same token, high (base) wisdom scores are typically not worth the cost, unless a character has a class that benefits from high wisdom. Even paladins and rangers, who do benefit from high wisdom, often do not have a base wisdom over 14, as that is all that is needed for their spellcasting.
A convention established by BioWare in the official campaigns is that a (modified) wisdom of 14 or more is required to access "insight" dialog lines, lines that allow the player character to deduce information from subtle observations of another character or the environment. This is not a universal rule though, and implementations in other modules may vary.
On the other hand, this "high" range for wisdom is defined in the core scripts (specifically
nw_i0_plot), so if a module does make a distinction between "normal" and "high" wisdom, the readily available "14 or more" criteria is likely to be used.
Cleric, druid, paladin, and ranger spellcasting is wisdom-based. This has several consequences. The highest spell level that these classes can cast is the caster's base (unmodified) wisdom score minus ten, while bonus spells are given to these classes based on the caster's current (modified) wisdom modifier. In addition, the wisdom modifier is added to the DCs of spells cast by these classes.