Whatever is a keylogger?

I am considered tech savvy but I admit I do not know what is keylogger. My friend MSN and asked me if I know what is keylogger. Off hand, I told her it may be some software that is used for the monitoring of our PC usage, just like how parents keep track of their children computer usage. Sort of a security measure.

However, both of us Google and found that I am correct!  So, you see, I am rather tech savvy, isn't it?  I am aware of such software and would advocate parents to consider it if they do not have the time to monitor their children all day.  For me, it is not necessary as I adopted the open door policy and everyone has a share of the PC so there is no hanky panky going on.