In passing, hijacking is where one passer decides to change what pattern they are passing and their actions transitions their partner into a compatible pattern. Collectively these are also known as “programming” because you are programming your partner. Most people use programming and hijacking interchangeably.
Introduction to passing 4-handed Siteswaps with video and schemes by Brook and links to more resources. Check this out if you want to finally understand 4-handed siteswaps and advance your passing!
Let´s start easy, funny and entertaining with vanilla siteswap, explained at the ‘Nerd Nite’ in Magdeburg, November 2014 by Alexander Leymann (in German, but the slides are very useful!). If you prefer further reading, here is the link to Allen Knutsons Siteswap FAQ