A variable is identified through a name and contains a defined value.
The value joined to the variable defines its type: for instance, a variable having a word inside is a string type. However, it is possible to edit the value of a variable by a new one of the same type, while it is not possible to give to a variable, that at first has such a value, a new value of different type.
A constant is identified through a name and has a certain value, unlike the variable, this value cannot be modified: then a constant can have only the value which has been initialized with.