Periodic Function
An Example of a periodic Function is a Square Wave. $ x(t)= x(t-T) $. As Seen in the picture below.As you can see below the function repeats itself every 2*pi*frequency
Non-periodic Function
An Example of a non periodic CT Function is an Exponential Function. $ x(t)\ne x(t-T) $ for $ T>0>t $ As Seen in the picture below.