Watch out for literary critics. They can get feisty.
Reader-Response theorists really don't like the New Critics, a bunch of mostly dudes who were all about the text. The New Critics They thought that the meaning of a literary work could be found in the work itself. According to them, you don't need to know anything about the social or cultural context of the work, or about the author's biography. And the reader? Who cares about the reader?
For the New Critics, the reader wasn't important, because in their New Critic-y minds, the reader had nothing to do with the actual meaning of the text.
According to Reader-Response critics, though, meaning isn't something that's just sitting there inside a literary text, waiting to be discovered. For them, meaning is something that's made as a result of the interaction between the reader's mind and the text. Reader-Response theorists argue that the reader is actually as important as the author.
One criticism Reader-Response theorists often get is this: if everyone reads differently, then how the heck can we come to any consensus about a literary work? If everyone has a different interpretation of the same text, that means that we can never agree about what the text's saying or doing, right?
Different Reader-Response critics would answer this criticism differently. There are those, like Norman N. Holland, who'd say: "Yes, we're all different, and yes, our readings are all going to be different. But that's okay. Why do we have to agree on what a text is telling us? There's no need for agreement."
And then there are other Reader-Response critics, like Wolfgang Iser, who'd argue that texts guide our responses to some extent. Yes, we each respond differently to texts, but our responses can't be that drastically different. To go back to the cake analogy: we can't make a carrot cake if we are given the ingredients for a cheesecake. Yes, we might each make the cheesecake differently, but at the end of the day it will be a cheesecake – our response as readers is determined, to some extent at least, by the ingredients that a text gives us to work with.