It's not easy to hide an Android application; they are usually displayed directly on the home screen. But it is possible, although it requires access to system files by way of rooting. Root access lets you change files that are otherwise locked, including apps and their locations. Unhiding an app won't be easy if you are not the one that hid it in the first place. This is due to security methods imposed by apps that hide them from view.
If you are new to Android phones, you might not realize that the home page you see is just an overlay. It provides a quick way to access your favorite apps, without having to scroll through the entire list. The rest of your apps are made visible once you click on the "Applications" icon in the bottom left corner. It is the one that looks like a tiny square with dots. Drag your finger across the screen to choose a blank page, then tap "Applications." Hold your finger down on an app to transfer it to that page.
Open "Manage Applications" for a more comprehensive list of your applications. This screen shows you which apps came from the market, saved on the SD card or currently running in the background. Tap "Downloaded" and market apps are organized in alphabetical order. Tapping "All" displays every app, even those you didn't realize you had. Tapping an app also allows you to clear default settings, clear its cache or uninstall it completely.
This type of app is designed to obscure private information from public view. Photos and videos can be hidden easily, but to hide apps the phone needs to be rooted. If you suspect apps are being hidden by another app, you may not be able to determine which one it is. Some of the more sophisticated versions install themselves as a "Volume Slider" or "Picture Viewer" to hide its true function. In addition to entering a password, you might have to press and hold a specific spot just to launch it.
It only takes about two taps to uninstall an app, so it is possible to uninstall it by accident. Tap "Market" and then the magnifying glass to search for the missing app. If it was a previous purchase, you'll find it quickly in the Menu under "My Apps." Install the app the same way you did previously and it will be shown under Applications along with all the others.