Ohhhh... I thought you meant what is it called. You need a double inc and double dec seperated by a few sts. You can do 2 single increases or decreases or do them as doubles. So for instance - k2tog, k3, inc inc, k3 ssk, and repeat. Or k2tog, *k3, yo, k1, yo (or k, YO, K in the same stitch) k3, sl 2, k1, psso and repeat from the *. The last repeat will be a ssk instead of sl 2, k1, psso. If you're knitting in the round just do it as *k3, yo, k1, yo (or k, YO, K in the same stitch) k3, sl 2, k1, psso and repeat from the *. You can also put more sts in between the incs and decs, like 4 or 6 or 7. And the increases can be done as M1, K1, M1, instead of YOs.
Here's an afghan pattern that's in ripple st, and I think Lion has other ripple blanket pattern too. Maybe even a scarf pattern.
Oops - forgot the link - http://www.knittingonthenet.com/patterns/afripple.htm