This is a little complicated:1. Buddha
A generic name, an appellative - but not a proper name - given to one who has attained Enlightenment (na mātarā katam, na pitarā katam – vimokkhantikam etam buddhānam bhagavantānam bodhiyā mūle ... paññatti, MNid.458; Ps.i.174) a man superior to all other beings, human and divine, by his knowledge of the Truth (Dhamma).
The texts mention two kinds of Buddha: viz.,
Pacceka Buddhas - i.e., Buddhas who also attain to complete Enlightenment but do not preach the way of deliverance to the world; and
Sammāsambuddhas, who are omniscient and are teachers of Nibbāna (Satthāro).
The Commentaries, however (e.g., SA.i.20; AA.i.65) make mention of four classes of Buddha:
All arahants (khīnāsavā) are called Catusacca Buddhā and all learned men Bahussuta Buddhā. A Pacceka Buddha practises the ten perfections (pāramitā) for two asankheyyas and one hundred thousand kappas, a Sabbañu Buddha practises it for one hundred thousand kappas and four or eight or sixteen asankheyyas, as the case may be (see below).VERY LONG ARTICLE (See Link immediately below)http://www.palikanon.com/english/pali_n ... buddha.htm