OS X Internet Recovery
Newer Macs include the ability to start up directly from an Internet-based version OS X Recovery. Your Mac automatically uses this feature when the Recovery System on the startup drive isn't available. For example, if your startup drive encounters an issue, or if your startup drive has been replaced or erased. Internet Recovery lets you start your Mac directly from Apple's servers. Starting up from this system performs a quick test of your memory and hard drive to check for hardware issues.
Internet Recovery initially asks you to select a Wi-Fi network and enter a network password when needed. Next, Internet Recovery downloads and starts from a Recovery System image. From there, you are offered the same utilities and options as the Recovery System on a startup drive.
Some Macs that came with OS X Snow Leopard can use Internet Recovery after installing OS X Lion or later and a software update.