It's usually called petal effect. There have been several threads on the topic. Here are links to a couple:
Thank you so much for sharing. Great links.
I have tried it and it is very easy. Just make sure you have a really good icing that is not too thin and lots of time and concentration. Make sure you have enough #12 tips and bags pre-filled with all the icing colors you intend to use. I love this idea!!!
You can also achieve this look by just using your same tip as piping out the dot without the offset spatula. So pipe out the dot, then drag it to flatten out. Repeat. This saves so much time and looks just as good.
When I do my cakes using the petal effect, I do one horizontal layer or row at a time, instead of doing the vertical columns. When I get to the end of the row, I angle that dot up, then begin the second row. This helps to make the back seem a little more un-noticable.