The iPhone and the iPad (as also the Motorola Droid and all the other Smartphones with their fancy virtual keyboards on the touch screen) do not support all possible keys in their virtual keyboards. A case in point is the backtick character. This makes it a problem when you need to enter the character in a text entry field of some app or web-site.
A simple but annoying way to deal with this is to do a web search for that character by name, find the character on some web-site and copy and paste it in to whatever text entry field that needs it. For your convenience I’ve provided this character on a separate line at the top of this post (to help work with the limitations of cut-n-paste on the iPhone/iPad).
Note that some of the virtual keys bring up a pop-up with additional keys supported when you keep you finger pressed on it.