The most fundamental of Hindu deities, is the Trinity of Brahma, Vishnu and Shiva - popular deities include Ganesha, Krishna, Hanuman and goddesses like Lakshmi, Durga,Saraswati.
Jagannath, Lord of the world, is the symbol of Vishnu. Jagannath' is a combination of two words 'Jagat' and 'Natha'. 'Jagat' means 'The Universe/World' and 'Natha' means 'Lord/Master'. So the name Jagannath literally means 'Lord of the Universe'. Puri is the dwelling place of Lord Jagannath so this place is otherwise known as 'Jagannath Dham' or 'Jagannath Puri'.
Lord jagannath is the presiding deity of Puri Jagannath Temple. In side the temple He is worshipped with his older brother Lord Balabhadra, sister Subhadra and the mighty Sudarshan Chakra (disk). Jagannath is Black (inscrutability) in color, Lord Balabhadra is white (enlightment) in color, sister Subhadra is yellow (goodness) in color and lord Sudarshan is red in color, hence representing all the four races of world.
In Sanskrit 'Ja' represents Jagannath, 'Ga' represents Balabhadra, 'Nna' represents Subhadra and 'Tha' represents Sudarsan. So Jagannath means the union of all four deities of the Jagannath Temple. His arms are parallel, hence willing to embrace the devotees from all over the world and his eyes are round with out any eye lids, hence looking after the welfare of his devotees with out any sleep.
Everything related to Lord Jagannath is Bada (any form of Greatness). He is known as the Bada Thakura (The Chief among all Gods). His Temple is known as the Bada Deula (The main temple among the temples). The road in front of the temple is known as Bada Danda (Grand Road). The Sea of puri is known as the Mahodadhi (Great Ocean). The cremation ground in Puri is known as Swargadwar (The Gateway to Heaven).