A Buddha is a person who attains full and complete enlightenment entirely through his own efforts and determination, unguided by another. All Buddhas have the same understanding, the same realization, but they do not all have the same abilities.
The Buddha of our era, Siddhattha Gotama, was extraordinarily gifted. The things he said and did had a profound effect on his contemporaries and indeed they are still moving people two and a half millennium later. However, there have been other Buddhas who, due to their gentle natures, their lack of communication skills or their particular circumstances, never taught what they realized, but lived their lives quietly and passed away unknown to those around them. Such Buddhas are called Silent Buddhas (paccekabuddha). One particular silent Buddha described his realization like this: "The envelope of the womb has fallen away from me, continued becoming is cut off, the grime of continued existence wiped clean, the ocean of tears dried up, the wall of bones broken down, there is no more rebirth for me" (Ja.III,377). Silent Buddhas were described as being like this: Their hair and beard are shaved, they are arrayed in a yellow robe, they do not identify with any particular family or tribe, they are free like a cloud blown by the wind and bright like the moon after an eclipse (Ja.III,377).