State

is a system's configuration, attributes, condition, or information content

temporary: changes with time

volatile: it will be lost or reset to some initial state if the system is switched off

simple example: a light, which is either on or off

complex example: electrical activation in a human brain while solving a problem

in computing states are usually discrete, with instantaneous transitions

HTTP is stateless

All HTTP requests are independent of preceding requests

Each HTTP response depends entirely on the information contained in the corresponding request

Advantage: allows a simple and efficient Web server implementation

Disadvantage: complex Web applications are rather difficult / complex