The term "UFO" stands for "Unidentified Flying Object." A vast majority of UFO-sightings can easily be explained. It usually involves either a natural phenomenon, or an "identified" flying object, like a weather balloon, or a sattellite.
Depending on the source, between two to five percent of UFO sightings involve real flying objects that are genuinely unidentified. In real numbers, those two to five percent still constitute a large amount of forty to fifty thousands of sightings every year! Yet there is a remarkable degree of consistency with regard to the shapes of the "spaceships" that people encounter. There seem to be six main categories, two of which look indeed like "flying saucers." A first type looks like an upside down saucer. Often it has a dome on top. A second type is similar, but looks more like two saucers on top of each other, the top one upside down. Again, these ships often have a dome on top. A third type consists of spheres or balls. Then there are the cigars, ships that are silvery in colour, and look like one giant cigar. Next are the triangular ships with pulsating lights. These ships are seen more and more frequently. Lastly, there are the ships that are oval shaped, or look like an egg. Other types of crafts - that, e.g., look like croissants or crescent moons, or that have geometrical shapes, have been encountered, too, but not as frequently as those other types.
It is believed that the saucer-like ships are used by both humanoid (mainly Pleiadian) and Reptilian / Grey species. Thus far, mainly greys have been seen near the triangular ships and humanoids near the cigar-shaped ships. The humanoids that occupy the croissant-like ships often identify themselves as Sirians. Still, insufficient data is available to make any definite assertions.