Serialisation describes the process of taking your (in memory) datamodel and writing it to a file. Later that file can then be read and restore the original data you were working with. Effectively the goal is to save the current state of your program so that you can continue at a later time where you left of.
A side effect of this process is the ability to send the data not to a file, but over the network to another computer that, running the same program, can then see the same data you are working on.
There are many ways of serialising your model: