What is a counter?

http://www.google.com/search?q=math+counter&hl=en&tbo=u&tbm=isch&source=univ&sa=X&ei=GR0cUaiCL6m9ygH9-4DgDg&ved=0CDMQsAQ&biw=711&bih=453

http://www.ehow.com/how_7835556_use-counters-math.html