IsBackground Property

Gets or sets a value indicating whether or not a thread is a background thread
All threads created by calling a Thread class constructor execute in the foreground by default
All threads which are part of a pool of worker threads maintained by the runtime execute in the background my default.

System.Threading.Thread myThread; 

myThread = new System.Threading.Thread(delegate() {}); 

myThread = new System.Threading.Thread( new System.Threading.ThreadStart(myMethod) ); 

public static void myMethod() 
{} 

myThread.SetApartmentState(System.Threading.Apartment.STA); 
myThread.IsBackground = true; 
myThread.Start()