Difference between $x and ${x}

Many times in shell scripts we would have witnessed two different forms of notations being used against variables: $x and ${x}. Are they both same or is there any difference between them? Let us discuss in this article:
Let us assign a value to the variable, x:

$ x=10

Now, lets try to display the value using both the above notations:

$ echo $x
10

Displaying using the second notation:

$ echo ${x}
10

As seen above, it does not look like there is any difference. But it is not so. The actual difference we will see now:

Let us try to join or concatenate the literal "y" along with the value of $x:

$ echo $xy
 

Nothing got printed for "echo $xy". Now, let us the second notation to display:

$ echo ${x}y
10y

What happened? When we said $xy, the shell interpreted it as being asked to print the value of a variable named "xy". Since there is no such variable "xy" being defined, a blank output. However, the second notation ${x}y is being interpreted as : print the value of x and concatenate it with the literal "y", and hence the result "10y".