Annealed glass is slowly-cooled after first being formed.  It’s left to rest at a temperature where it becomes too hard to manipulate, but soft enough for any stress points to melt away.  This steady, consistent temperature at the earliest stage helps the glass resist shattering and mechanical shock during installation.  Annealed glass is a commonplace, inexpensive and tough material, but it isn’t quite as durable as tempered glass.