Oíche Samhain, Halloween, and Ireland's ghosts

Oíche Samhain was celebrated on the eve of November 1st.  It is  also the Irish name for the month of November. The festival was a time when people believed the veil between the worlds of the living and the dead was thin, and that spirits could cross between worlds more easily. 
It was a time to welcome in the harvest and welcome in “the dark half of the year.” For the Celts, the Samhain festival was the most significant of the four quarter 

Celebrations included: 

Lighting bonfires 
Dancing and singing 
Feasting 
Leaving treats out for fairies 
Children playing games to entertain the dead 
Adults updating the dead on the past year's news 
Leaving doors and windows open for the dead to come in 
Using particular foods for divination or soothsaying