What is the definition or description of: implantation?

Implantation: One common meaning refers to the process by which an embryo attaches to the uterus of a woman so that she is pregnant. Many think of it as 'sticking.' implantation in humans always occurs when the embryo is between 6-7 days old. A very popular concept on the internet now in 2012, 'implantation bleeding, ' is speculative and mostly not useful.