This day, always on a Monday, marks the descent of the Holy Spirit to the gathered disciples, fifty days after Pascha (Greek Easter). Aghio is the neuter form of the word that denotes holiness/saintedness which precedes the name of the sainted person, and is used in this case with the word for spirit, which is neuter. Some chapels bears this name, where this day is duly celebrated.
This female saint is the protector of crops, her day much celebrated in farming areas. There are also villages named for her, where the entire village celebrates her day.
These two saints (Peter and Paul in English) share a joint feast day, which is often celebrated conjointly with Aghia Apostoli, the following day.
The day of the Holy Apostles.
There are thousands of hill or mountain tops all over Greece with churches, chapels, or shrines named for the Prophet Elijah, marking the highest point in the region/island. On this day, it is customary for local people to hike to that peak and feast there. Elijiah was spiited away by chariot to heaven (swing low sweet chariot - coming to carry me home)
This saint's name is the same as the Greek name of the day Friday, and means 'preparation', referring to the coming Sunday, with church bells tolled on the Saturday evening.