How to make a PHP variable accessible from every webpage?

Is it possible to create a variable, set its value through a webpage and make it accessible from code in other webpages?

If yes, how is this done in PHP?

Will the variable have a life time in memory if it is not used for a long time?

Answer

1. Use session or cookie varibles (or)
2. declare in common file (or)
3. Try global variables (or)