whats this pipe?

[crazypainter]

I noticed a split in this pipe when I was under the bonnet checking fluids etc. Actually it looks more like it has been accidently sliced with a knife or something. I dont know if it goes all the way through at all, doesnt look like it does, but I am wondering what it is for and the implications of it leaking?

thanks

 

[snowball1969]

just replace it. wouldn't even try to work out what it does