In PHP, the scope of a variable refers to the areas of your code where the variable is visible and can be used. There are two types of variable scope in PHP: local and global.

1. Local variables: Local variables are variables that are defined within a function, and are only visible and accessible within that function. These variables are also known as function-level variables, and are created using the “local” keyword. For example:

function myFunction() {
$localVariable = "Hello"; // Local variable
echo $localVariable; // Outputs "Hello"
}

echo $localVariable; // Throws an error, as $localVariable is not defined outside of the function

2. Global variables: Global variables are variables that are defined outside of any function, and are therefore visible and accessible from anywhere in your code. These variables are also known as script-level variables, and are created using the “global” keyword. For example:

$globalVariable = "World"; // Global variable

function myFunction() {
global $globalVariable; // Accessing the global variable
echo $globalVariable; // Outputs "World"
}

echo $globalVariable; // Outputs "World"

It is important to note that global variables can be accessed from within functions, but local variables cannot be accessed from outside of their respective functions. This is because local variables are only defined within the function in which they are created, whereas global variables are defined at the script level and are therefore visible to all functions and code blocks.

Additionally, it is generally considered best practice to use local variables whenever possible, as they can help to reduce the risk of conflicts and errors in your code. This is because local variables are only defined and used within a specific function, and are therefore less likely to interfere with other parts of your code. However, there are certain situations where global variables may be necessary, such as when you need to access a variable from multiple functions or code blocks. In these cases, it is important to be mindful of the potential risks and limitations of global variables, and to use them responsibly.