The difference is that at each instant in time, the 180-degree delayed wave has exactly the opposite value of the original wave. 

If $y_1(t) = \sin(2\pi{}ft)$ and $y_2(t) = \sin(2\pi{}ft + 180^\circ)$, then $y_1(t)=-y_2(t)$ for all t.

If you are talking about a sound wave, then whenever one wave has a minimum of pressure, the other has a maximum and vice versa.

As other answers said, this difference is not perceptible to human hearing because the ear is not sensitive to phase differences or delays on the scale of a single cycle of a sound wave.

What is fundamental difference between wave and its 180 flip phase?
I have a list of some strings and I want to create a list for each of them dynamically inside a loop.

The main idea is to get each string from this list through the loop and create a list with this string as a name. Then add some data to it. 

Example:

   List&lt;string&gt; names = new List&lt;string&gt;(); // this is the main list with strings

   foreach (string nm in name)
   {
     // Here create a new list with this name
     // Add data to the list
   }  

   // Now, compare all of them to find duplicate data

   // Give message if any duplicate data found


Update:
Basically, I am going to add data to the list using some database APIs on runtime and the string names are the keys in that API. So with each name in the main list, I will retrieve some data from the database, create a list with that name and add data to it. Later we will compare them together. So the basic question is still how do I create these lists at runtime.
