A sequence is a set of numbers that fit a pattern. For example 2,4,6,8,10 all go up in a sequence of two. In the real world sequences occur every second, there are sequences taking place to run the device in which you are reading this very sentence off. Looking at the natural world a pinecone follows the Fibonacci sequence in the way it develops the pines on the outside. But why the hell is the relevant to me, I bet your asking. If you think a leap year occurs every four years and so the sequence would be 2012, 2016 and then 2020. Think due to a sequence of events you get an extra day every four years.
Types of Sequences
Example Questions explained
Check the Spec'
AQA Mathematics (8300) 3.2.4 Sequences