What does the celebration of samhain signify?

In Wiccan wheel of the year, Samhain signify the beginning of the winter, the end of the light half of the year. This is the time when the power of the Sun dies for the northern hemisphere. Therefore Samhain is considered as the death of the Horned God, until he Resurrects/Reborn on the Yule day.

This day is celebrated with Farewell and Honoring the dead.