If it really disappeared and you just didn't file it in a folder, you can reset your entire layout in Settings - General - Reset - Reset Home Screen Layout
This will remove your folders and reset the display of all your icons
Regarding your question, do you have lots of apps and have you filled all 11 pages of your screens. If you have, the apps are still there but there isn't a space for them. It would be time to arrange folders. Let us know. You can search for it, swipe to the right through your screens until you come to the search screen, do a search for it here.
The IPad Forum is a community of members from all walks of life and from all over the world coming together to share our experiences and to help each other learn about this wonderful piece of technology the Ipad. There is a wealth of information already here in the many threads we have so doing some searches will answer most of the questions you have. If then you cannot find the answer you are seeking then by all means post your question. There are many friendly and informed members here only too willing to help you.