What is meant by 'intertextuality'?

A key part of A-level English Literature is understanding the context of texts. We should note that when we are reading something, what we are reading is very often inseparable from a network of ideas and influences that surrounded the author, and subsequently surround the text. Therefore, when reading a novel, it can help to think about it in relation to other texts, and we may even notice things in our reading that remind us of other works we have read. This is intertextuality, and it can come in many different forms, such as: parody of another work; quotation; allusion; the reflection of ideas from a different text, etc.

Intertextuality could even present itself in similarities in characters, for example, some might argue that Mary Shelley's Victor Frankenstein shares some likenesses with Goethe's Faust. Faust is a character who sacrifices much in the pursuit of knowledge, just like Victor Frankenstein, leading us to even be able to call Shelley's Frankenstein a 'Faustian' novel, making it a prime example of intertextuality.