Among the most important concepts of the programming is the concept of variable. Like any language, PHP handles data. For a dynamic site, these data are variables. In addition, they may be of different types, such as text string, as you have used the echo statement in the form of whole or decimal numbers or as true or false boolean values (TRUE or FALSE). These basic types are the most used, but there are others who may be compounds types, such as arrays and objects, or specific types, as resource or NULL. . We will see that the variable part of the mechanisms which make a dynamic application. Let's get into the thick of it.