Tzedakah is a Hebrew word which has a variety of translations. The most common is charity, but the root and related words mean justice or righteousness.
There are many traditions around giving tzedakah or charity. Some examples are contributing to a charity box each Shabbat or in religious school. Some families keep a box at home; some congregations keep a box at the entrance to the sanctuary. On the High Holidays, some congregations hold food drives. Donating at Purim is an old tradition. Another common tradition is to give a donation to a charity related to the interests of a loved one who died in that person's memory -- both when the initial loss occurs and sometimes as an annual memorial. It's a way to honor and continue that person's good deeds.
In Hebrew, it is צדקה.
Maimonides listed 8 "degrees" of charity. The lowest is someone who gives, but unwillingly. The highest is when you help some one to be able to take care of him or herself.
One of the differences between tzedakah and charity is that while charity is a choice, tzedakah is required of everyone, even the poor. The Greek root of charity means from the heart. It's seen as a kindness. But giving tzedakah is doing what is right, what is just and required.