Intertexuality

Intertextuality is using one piece of work to provide context for another. An object, be it a piece of art, a garment or even a person is given meaning by its creator. There are other theories in that the context of the piece is given by the viewer.
Context and intercontextuality are important as they are what define for the viewer the overall message of what they are seeing. This can be played straight, such as a nun wearing a habit and a crucifix, or it can be used to askew social norms and make bold statements, such as artists like Madonna or Lady Gaga wearing the same items, Items and garments are given meaning by the situation that they are placed in and the other visual or sensory cues that they are partnered with.
Intertextuality is important in all aspects of life and is used regularly in fashion. It has been used famously by many celebrities often by incorporating controversial slogans or religious objects in the way that they dress. It has also been used to make a statement in a similar way by designers from the last few decades. This act of using a object in a way that it isn't meant, or by adding to it, for example the way the Sex Pistols shook up the image of the Queen, can be a political, religious, or just plain rebellious statement on the part of the individual or the designer.
Another theme that has arisen from the theory and use of intercontextuality is bricolage. Bricolage is essentially taking a selection of mismatched styles and using them in such a way that it creates a suitable ensemble. For example, steampunks mix the grittier side of punk with the elegance, beauty and clothing design of the Victorian Era. On paper, these two styles don't work together particularly well, with each being the overall antithesis of the other but through the use of clever styling and an understanding of context, amazing outfits are put together. This act of mixing styles and removing aspects from one to another is also a way of making a statement, this further removal of the subculture from the socially acceptable norm. 
I'm a great believer in the theory that nothing is every original. Everything we do, everything we think, everything we design and create is made from influences around us. The author Austin Kleon published a book entitled 'Steal Like an Artist' and it details how influence is all around us and how we should note other people's work in regards to not it's overall quality as a piece, but breaking it down into factors that we like and dislike and then go on to use the factors that we enjoy or approve of in our own work.