Android Market

Like Apple's App Store, Google has its own mobile app store called the Android Market.  It has a vast array of apps that can be installed on your mobile phone but the biggest difference is that Google doesn't vet each application that is published in the Android Market.
This means you as the end User need to be vigilant with the applications you download and install on your precious and personal mobile device.  Most of the time Google will go on a cleaning spree and remove apps that are harmful but some apps do get through, so being cautious and reading reviews is a good start when deciding what app to install on your phone.

For more info read: Being street wise with apps on the Android Market