Functions : A function is that they are reusable; if you have a task that needs to be performed a number of times, a function is an ideal solution.
User defined Function : Besides the built-in PHP functions, we can create our own functions. A function is a block of statements that can be used repeatedly in a program.
System Define Functions : A function is already created by system it is a reusable piece or block of code that performs a specifi c action. Functions can either return values when called or can simply perform an operation without returning any value.
Parameterized Function : PHP Parameterized functions are the functions with parameters or arguments.
Array : An array is a special variable, which can hold more than one value at a time of same type. It’s a collection of homogeneous data
Associative Array : Associative arrays are arrays that use named keys that you assign to them.
Indexed Arrays : The index value is assigned to each array element.
Multi-Dimensional Array : A multidimensional array is an array containing one or more arrays.