Kimcha D'pischa means "flour for Pesach." In other words "Kosher for Passover Flour." This refers to the age-old custom of giving charity before Pesach to the city's poor so they will be able to afford all their Passover needs.
This custom is ancient, first mentioned in the Jerusalem Talmud. The idea behind it is that it was hard to find "Kosher for Passover" flour to buy during the holiday. It is important that also poor people, who live on a day-to-day basis, should not lack food to eat on Pesach, due to not being able to afford flour for baking matzahs. Hence began the custom to distribute flour before Pesach.
Today, most people don't bake their own matzahs, so kimcha d'pischa has been adjusted to meet the needs of the poor people of today. All over the world Jewish communities give money to the needy before the holiday so they can prepare. In many communities food supplies are distributed for free or at great discount. In my community, charity organizations give money to the supermarket to credit the accounts of needy families, in addition to food distribution and cash donations.
It is said that before Pesach there are two types of people: Those who give kimcha d'pischa and those who get. In other words, anyone who can is obligated to help the needy meet their holiday expenses.
It is very meritorious to make a donation to a kimcha d'pischa organization, in your community if possible. You may contact the Gateways Organization at gatewaysonline.org for assistance.
There is a wonderful story about how charity money is distributed before Pesach. A woman once approached the Rabbi of the city of Brisk, Rabbi Yosef Dov Soloveitchik, with a strange question. She wanted to know if one could use milk instead of wine for the four cups of the Seder. She explained that she could not afford wine. He answered her by giving her a large amount of money. Asked the Rabbi's wife, "I understand you gave her money because she can't afford the wine, but why so much?"
Answered the Rabbi, "If she wants to drink milk at the Seder, it is obvious she has no meat for Pesach (as there is a prohibition to eat meat and milk at the same meal). So I gave her enough to by wine and meat for the entire Holiday."