Hi pals
I have herd about UFO a lot please tell me what is that ?

Unidentified flying objects- they are the vessels that supposed aliens from other planets travel in.

Hi,
Crankiebabie gave you the words for UFO. Here is one of many, many links:
http://www.qtm.net/~geibdan/framemst.html

It has some explanations about UFO's. You can also do a search online for Roswell, NM. This is the town where many of these Unidentified Flying Objects have been reported. There are also questions about a "secret" Federal Gov't research complex located there, with alleged aliens in it.
Many people have reported seeing lights in the sky at night, very, very fast moving, coming together from 3 other lights into one light, then moving away so fast, it's gone in a heartbeat.

Despite the little evidence supporting extraterrestrial beings, UFO buffs are notoriously known for their slogan, "We are not alone.". Belief in aliens in UFOs is akin to belief in supernatural beings. Like other beliefs, while the probability may be low, belief requires faith over reason.

History of UFOs (http://www.ufo-gifts.com/history-of-ufos.htm)