Zakat is a term originated exclusively for people who follow Islam. It's purpose is to provide financial assistance in the furtherance of the cause of Islam - in any way, shape or form. The "charity" to which zakat funds is given must be an approved charity - approved according to Islamic jurisprudence under the Sharia law. Examples of a zakat approved fund would also include any fund that was created to help Muslims who are in need to follow Islam. Another zakat approved charity would include an organization that is set up in a kuffar (unbeliever in Islam) country to bring the unbelievers to Islam (dawa).
Zakat is quantified as a preset percentage of annual income. It is commonly given around Ramadan especially, and many zakat-approved funds act as a mask to fund jihadist activities - which often translates into terrorism for the unbeliever.
There is no such thing as a charity for the unbeliever in Islam. Humanist / secular charity as understood by occidental citizens is a Judeo-Christian concept and it applies to every human being regardless of religion, sex, race or age creed. Some are earmarked but the overall concept applies without discrimination.