I was reading Ubuntu Server documentation, the virtualization part, about UC, ando also found about MAAS, is UC the same as MAAS? Could somebody please explain me the diference?
Ubuntu Cloud and MAAS are different things - different layers if you like.
MAAS is a low-level layer which deals with physical hardware. It is for deploying the base level software to a rack of servers quickly and easily. It can then work in conjunction with juju to deploy particular services (e.g. web servers, databases) to that hardware. This could be for all sorts of applications (not just clouds).
"Ubuntu Cloud Live" is really the top-layer full cloud service image, built with OpenStack.
You can find out more specifics on MAAS at maas.ubuntu.com