3-pipes is a feature that allows users to have 3 Monitors plugged in. It is present at 3rd Generation Intel® Core™ processors with Intel® HD Graphics (codenamed IvyBridge) and 4th Generation Intel® Core™ processors with Intel® HD Graphics (codenamed Haswell).
For other platforms only Dual outputs are supported.
In order to get 3 screen outputs at Ivybridge you shall use 2 Display Ports + any display with some limitations on modes supported.
Easy way to verify what modes are supported is using this script.
Haswell 3-pipes is less restrictive than Ivybridge. You can have 3 screns with
* 2 Display Ports + any display
* 1 Display Port and 2 HDMI or DVI
* 1 VGA and 2 HDMI or DVI
and no restrictions on mode combination.