What is intertextuality?

Wikipedia provides an excellent overview of intertextuality. I've highlighted key points below.

The term implies direct connections between texts, whether intentional or not, but in a more general sense, everything we write has connections with what we've previously read or heard. We recombine words and phrases to express our thoughts. In most cases, "intertextuality" per se is more specific than merely recognizing common words. 

https://en.wikipedia.org/wiki/Intertextuality

Here is the introduction:

Intertextuality is the shaping of a text's meaning by another text. It is the interconnection between similar or related works of literature that reflect and influence an audience's interpretation of the text. 

Intertextuality is the relation between texts that are inflicted by means of quotations and allusion.^[1] 

Intertextual figures include allusion, quotation, calque, plagiarism, translation, pastiche and parody.^[2][3][4] It is a literary device that creates an 'interrelationship between texts' and generates related understanding in separate works.^[5] 

These references are made to influence the reader and add layers of depth to a text, based on the readers' prior knowledge and understanding. The structure of intertextuality in turn depends on the structure of influence.^[6] 

It is also a literary discourse strategy utilised by writers in novels, poetry, theatre and even in non-written texts (such as performances and digital media).^[7] Examples of intertextuality are an author's borrowing and transforming a prior text, and a reader's referencing of one text in reading another.

Intertextuality does not require citing or referencing punctuation (such as quotation marks) and is often mistaken for plagiarism.^{[8][page needed]} 

Intertextuality can be produced in texts using a variety of functions including allusion, quotation and referencing.^[9] It has two types: referential and typological intertextuality. 

Referential intertextuality refers to the use of fragments in texts and the typological intertextuality refers to the use of pattern and structure in typical texts.^[10] 

However, intertextuality is not always intentional and can be utilised inadvertently. 

A distinction can also be made between iterability and presupposition. Iterability makes reference to the "repeatability" of certain text that is composed of "traces", pieces of other texts that help constitute its meaning. Presupposition makes a reference to assumptions a text makes about its readers and its context.^[11] 

As philosopher William Irwin wrote, the term "has come to have almost as many meanings as users, from those faithful to Julia Kristeva's original vision to those who simply use it as a stylish way of talking about allusion and influence".^[12]