Halloween and dressing up occurs in October in the United States, but in Europe and South America (Rio) it is in February. So here are some things about how we celebrate it in Greece, including a bit of linguistics, folklore, and religion.
According to one view, the word "carnival" comes from early Italian carve + levare, which means "take away the meat" (carne). The Greek word for it is apokreea (stress on the last -a-), which again means "away from meat." In both Orthodox and Catholic religions, the focus is on eating what meat is left in the house before Lent (the traditional period of fasting before Easter) starts.
Greek carnival is a combination of religious and pagan festivities. Following the Church, there are three weeks dedicated to gradually reducing the consumption of certain foods up to the beginning of Lent. In these three weeks people should also celebrate and have a good time before starting the fast, a period of repentance. Two are the high points of this season: the Thursday of the first week, which is dedicated to eating meat, is called tseeknopemptee: pemptee is the name of the day (Thursday or the fifth day of the week) and tseekna refers to the smell of charcoaled meat, what you smell at barbecues. On that Thursday night people go out to tavernas to celebrate and drink and have a good time; you can smell tseekna everywhere.
The last of the three weeks is dedicated to the consumption of dairy products and fish and the Monday just after it is called Clean Monday, something like Shrove Monday, which marks the beginning of Lent. On this Monday we should not eat meat or dairy products - we should be "clean" of all that. Only shellfish is allowed, and people go out to the countryside and have picnics and fly kites since the weather is usually permitting :). During these weeks people dress up and play pranks. Parades are held in all the cities. Dressing up is a pagan custom that has to do with scaring away the evil winter spirits before spring comes.
How all this is connected to the way people lived:
According to Professor N.S. Margaris, all these traditions are closely related to the way people lived. Sheep and goats usually breed in January. Because there was lots of snow on the ground, shepherds could not take them out to the pastures and were forced to reduce their number: tsiknopemptee is a relic of this tradition. After that, spring comes and there is plenty of grass; eating meat is thus forbidden up to Easter so that sheep and goats can grow.
On two of the Saturdays during this period people honor the dead. In many places in Greece people cook pasta. Now, the food that is given to those who come to wake the dead is called makareea, which means "blessing." According to one view, the word "macaroni," a kind of pasta, derives from makareea, or makareea + (e)oni(a) [eon] = "eternal blessing." And all this time you thought that pasta was Italian? :)