Zakat or sadaqah al-Fitr زكاة الفطر is an ordered charity given to the poor at the end of the fasting in the Islamic month of Ramadan.

Zakat al-Fitr زكاة الفطر or sadaqah al-Fitr صدقة الفطر or al-Fitrah الفِطرة is charity given to the poor at the end of the fasting in the Islamic (holy) month of Ramadan. (Source).
It is an obligation for all Muslims or more precisely on any person regardless of age and wealth if the costs of living at least for the 'Id day are covered, which must be fulfilled at the last few days of Ramadan and before the 'Id prayer.
It shouldn't be confound with the zakat obligation on wealth which can and must be payed at any time of the year if its required condition are fulfilled.