"The process in which multiple addresses are created on a single network interface, is known as "IP Aliasing". IP Aliasing will be very much useful when you need multiple IP addresses to set up multiple virtual sites on Apache making the use of only one network adapter. The most important advantage of IP Aliasing is that you do not need one hardware per IP Address, rather you can generate a pool of virtual network interfaces (i.e. Aliases) on a single device."
Read More at YourOwnLinux.