The implied reader is the person (or group of people) that we infer a text was made for. We base this inference on the text producer’s decisions about language, narration, characters, plot, structure, form, layout, mode, context, genre, etc.
In literary theory, a text is anything that we can use to communicate information, messages, stories, ideas and feelings. It can be consumed, analysed, interpreted and understood by us and other people.
The text receiver is the person (or people) who reads, watches or listens to the text. They rely on the cues and devices in the text to help them interpret it.
A text producer is the person (or people) who creates the text. They use the tools at their disposal to make something that other people can interpret and derive meaning from.