Post your Queries on Goddess Durga

A tiger symbolizes unlimited power. Durga riding a tiger indicates that She possesses unlimited power and uses it to protect virtue and destroy evil. The eighteen arms of Durga signify that She possesses combined power of the nine incarnations of Lord Vishnu that have appeared on the earth at different times in the past. The tenth incarnation, the Kalkin (a man on a white horse), is still to come. Thus, Goddess Durga represents a united front of all Divine forces against the negative forces of evil and wickedness. The sound that emanates from a conch is the sound of the sacred syllable AUM, which is said to be the sound of creation. A conch in one of the Goddess's hands signifies the ultimate victory of virtue over evil and righteousness over unrighteousness.
• Other weapons in the hands of Durga such as a mace, sword, disc, arrow, and trident convey the idea that one weapon cannot destroy all different kinds of enemies. Different weapons must be used to fight enemies depending upon the circumstances. For example, selfishness must be destroyed by detachment, jealousy by desirelessness, prejudice by self-knowledge, and ego by discrimination.

Source - http://www.koausa.org/Gods/God1.html