I think this is what the OP is asking about, and I think the quoted sentence is misleading. Dazed, stunned, prone, deafened, removed from play, marked, blinded, deafened, dominated, dying, grabbed, helpless, immobilized, petrified, restrained, slowed, surprised, unconscious and weakened are conditions that can be part of an effect. But an effect is a state imposed on a character or monster as a consequence of the use of a power (my opinion). This distinction is not clearly made in any of the books as far as I know, but the rules compendium lists those states in the subchapter called conditions, and the books consistently refer to other imposed states as effects. For example, the defense penalty and healing imposed by Astral Seal is an effect but not a condition.1. Status effects are things like dazed, stunned, prone, deafened, blinded.
Rules Compendium said:effect: The result of a game element's use. The damage and conditions caused by an attack power are the power's effects, for instance. Some powers have "Effect" entries, which contain some but not necessarily all of the powers effects. In an attack power, the effects of such an entry are not contingent on a hit or a miss.
What exactly defines what is an effect? Dazing, stunning, blinding, etc, etc are pretty straight forward, but what about knocking someone prone, push/pull/sliding someone, or gaining CA on someone? Are these considered to as "applying an effect" on your target?
Why do you ask?
It sounds to me like you clearly have some more-specific question in mind. Just ask it.
Specifically, there's either an item or a feat that provides you with a +2 bonus to your AC if you have an effect applied on the target who's attacking you. So, if you, let's say, daze them, i accept that you get a +2 AC vs their attacks, but what if you knock them prone? do you get the bonus? what if you gain CA on them, do you gain the bonus to AC?
I'm pretty sure it was a weapon enchantment, but not 100% lol
Please find the specific item or feat. At the moment, your question is meaningless because there's no situation in which it applies.