Writing is a skill and activity that so far seems to be uniquely human. The ability to create a series of external carved or painted symbols to represent either ideas or spoken communications has not been observed in other animals so far. Could other animals have the capacity for writing a language?
Dispilio tablet indicates one the first recorded evidence of writing. image: wikipedia
Writing is a form of technology for storing information that can be passed onto another generation.
Writing is a technology because it uses physical tools to imprint onto a medium.
For example a pen is a tool that uses ink pigment to leave a trace impression on a medium like a piece of paper.
A stick for example is able to scratch a symbol onto a medium that is soft enough. like a clay tablet or a piece of wood or bark.
Writing is about leaving an impression on a medium that can be viewed later. It's a way of storing information.
Writing is also a key precursor to mathematics. Some of the first forms of mathematics would have required recording symbols that represent numbers most often for the purposes of accounting and tax collection in early civilisations.
The content produced by writing can be enormously varied, from stories, records, accounting, navigation in the form of maps. Collections of writing are often stored as books or other mediums.
Writing with light is known as photography
The ending _graphy or _graph usually refers to the process of writing in some sense, in particular recording of information. For example a cardiograph is a mechanism for recording the activity of the heart.