This is one of the most powerful versions of an ancient sort of spell known as the "breakspell". It allows the caster to shatter one on-going spell (almost any spell with a non-instantaneous duration).
When a wizard casts this spell, he mentally chooses a spell effect within range (or the general area of a spell effect if the effects cannot be seen) and says "Cease" (some wizards point at the area, but this is not necessary). Instantly an invisible, blue throbbing crystal of magical energy springs from the wizard, and swerves off toward the spell. It then proceeds to burrow itself to the center of the magical energies, and after but a few moments pause, it explodes, shattering the spell by disrupting its aura. Note that this all takes less than a second, and all that the wizard sees is the cessation of the spell effects (and whatever consequences might come of that).
A wizard can shatter most spells instantly, without fail. There are but two exceptions to this rule. The first is those spell levels that the wizard normally couldn't cast. In example, a 12th level wizard can cast up to 6th level spells; those spell levels that he can't cast are 7th - 9th. In these cases, the spell receives a base saving throw of 16, with a +2 bonus (-2 applied to the base) for every spell level away the wizard is from being able to cast the spell.
The second exception are those spells with a single creature (i.e., Charm Person) or multiple single creatures (such as Haste) for the area of effect. These spells have more stable auras, and they check for all purposes described above as 1 spell level higher. A wizard may shatter spells that are effectively 10th level automatically at his 20th level of experience.
There are some conditions placed on the types of spells that can be broken. They must have a duration other than instantaneous, and it must be active at the time (an inactive Symbol spell cannot be broken, and hanging spells can rarely be... though it is possible to break the spell that hangs them). It must have a discernible (but not necessarily visible) area of effect; those that effect a large area (like Reverse Gravity) are the most obvious. Even Spell Turning and Walls of Force are susceptible to this spell.
There will be, however, some spells that meet these conditions that still cannot be broken. Anti- Magic shell is a prime example, as is any type of magic deadness. Some powerful protective spells (such as Prismatic Sphere) might be harder to break at the D.M.'s option, perhaps only destroying one layer at a time. Shattering some powerful mental effecting spells (like Geas) may cause insanity. D.M.'s should use their best judgment in such cases.<