Scrying is a magical technique which grants the user the ability to see events within their mind. While a mage is scrying something, they enter a trance which lasts only about as long as the vision. The simplest exercise is scrying an event which is nearby and currently happening. With more and more experience, more techniques can be mastered. A talented scryer can see distant events, things which happened in the past, and even occurences which only exist in the minds of others (although there is a difference between scrying someone's mind and reading it). Skilled scryers can move their point of view, allowing them to simply see things from a different angle or even to keep someone under surveilance for days.
Scrying is a basic technique, but the higher levels of this art are a challenge to master. Few mages have the patience to train their scrying skill to a useful level. However, powerful spellcasters such as the Dragons and Aimee were able to learn much about things happening in the world without ever actually leaving the privacy and comfort of their residences.
There also exist scrying pools, which is water enchanted by a powerful mage to view a distant locale, and scrying orbs, which do the same in a large gem.