Rails -- definition 60/40, turn down,etc

I hear more references to rail shapes than you can shake a stick at. I know hard from soft, and know what I am looking at when I’m look’n at it – but what are the definition, and implications of the following: 1) 60/40, 50/50 – the number thing? 2) Tucked-under? 3) Turned-down? 4) Over-easy? 5) Others Thanks Shine http://users2.fdn.com/~shine