Personalisation is where websites show you specific content dependent on data they have about you. Like showing you information about floral dresses because they think you’re a woman, or more articles about Bernie Sanders because you’re viewing from the US.
This technique is increasingly common across the web. It is used to make content more relevant to you, to get you to buy more, or to be more generally persuasive.
It usually happens invisibly – you don’t know why you’re seeing some content, and not other content.