Literally, the Buddha means the one who has attained Enlightenment. But such an interpretation, with every due respect to a linguists query, is not of much effect to a reader or an audience interested in the stories of the Buddha or the Buddhas. As the meaning of the word lies in its use, we must, therefore, try to discover the original meaning of the term as is specifically and contextually used in the Buddhist corpus for its definite connotative comprehension.
The Pali commentaries state that there are four categories of the Buddha.
The first category is designative to the Sammasambuddhas or Sabbannu Buddhas. A Sabbannu Buddha is gifted with the ten powers and has the mission to proclaim the saving truth to all beings for their Nibbana. He is therefore known the Sattharo by way of the above characteristic. Further, because a Buddha plays the most important role of a pre-eminent person he is styled as the Bhagava. He is compared with the Universal Emperor; and a lion (simha ). He is called a physician because he diagnoses the cause of suffering and prescribes the medicine; a Kinsman of the Sun (Adiccha-Bandhu) as he dissipates the darkness of ignorance; aBuddha Vira as he gives protection to all; an Anuttara, as he excels all; a Brahmana (though born in a Khattiya/Chatriya family) because he carries on the blessed tradition and excels in wisdom; self-control; and virtue. In brief, a Buddha is superior to all other beings - human or divine - by his knowledge of the truth.
The second category of the Buddha is that of the Paccheka Buddha, which is designative of the progressive ones but not bound by the pledge to preach the Way of Deliverance to the world.
The third category of the Buddhas is referent to the Chatusaccha Buddha, who has damaged the mental defilements or asavas .
At last, we also come across the category of the Bahussuta Buddha designating a learned person.