Symbolic meaning of pigs varies according to region & culture.

In earlier cultures such as ancient Egyptian the pig (sow, specifically) was considered a Great Mother and were symbols of fertility and abundance.  Here the pig was sacred to Isis, who embodied fertility. 

To the ancient Celts, the (sow) pig was also honored as a mother provider figure.  Celtic lore tells of Manannan, who owned a heard of pigs that never dwindled – they were forever replinishing their numbers. As such, in Celtic symbolism pigs remained icons of abundance.

Also in ancient Celtic beliefs, the pig was associated with Keridwin and Phaea who were both fertility moon goddesses.

The pig was also a symbol of virility, strength, and ferility in ancient Chinese cultures.   The boar is even among the animals in the Chinese zodiac where it is considered a symbol of sincerity, honesty, and determination.

In Hindu symbolism,  the pig is linked to Vajravarahi, the female consort of Vishnu.

The Greeks would sacrifice pigs to deities who pertained to farming and agriculture (Demeter, Ares, Gaia) this was to bring about bumper crops and insure favorable growing seasons.

Native American cultures (plains tribes) associated the pig as a harbinger of rains and as such, the symbolic meaning of pigs here is also linked to abudance, fertility and agriculture.

On the other hand, the pig is a symbol of ignorance in Buddhism.  Indeed, a black pig is illustrated on the Buddhist wheel of existence where it represents one of the three illusions of man in the Buddhist philosophy:

• illusions of thought & desires
• illusions innumerable as particles of dust and sand
• illusions about the true nature of life

All of these are said to prevent man from attaining Nirvana in the Buddhist tradition.

The pig is a symbol of sloth (laziness) and/or greed in ancient Christian symbolism.

Jewish, Moslums and Islamic cultures view the pig as unclean and they are forbidden to eat pork.

In dream symbolism the domestic pig indicates fertility, yet a wild pig is a symbol of lust & overindulgence.  If in your dream you are feeding a pig, this is supposed to be a symbol of good luck.  If you are being attacked by a pig, it may be a message you are being materialistic or greedy about something.