Differences between constants and variables in php

Differences between constants and variables  in php

• There is no need to write a dollar sign ($) before a constant, where as in Variable one 

has to write a dollar sign. 

• Constants cannot be defined by simple assignment, they may only be defined using 

the define() function. 

• Constants may be defined and accessed anywhere without regard to variable 

scoping rules. 

• Once the Constants have been set, may not be redefined or undefined.