Per IRS Publication 526 Charitable Contributions, on page 2:
A charitable contribution is a donation or gift to, or for the use of, a qualified organization. It is voluntary and is made without getting, or expecting to get, anything of equal value.
On page 3:
Generally, you can deduct contributions of money or property you make to, or for the use of, a qualified organization. A contribution is "for the use of" a qualified organization when it is held in a legally enforceable trust for the qualified organization or in a similar legal arrangement.
The contributions must be made to a qualified organization and not set aside for use by a specific person.
Examples of Deductible Charitable Contributions:
Money or property you give to:
Expenses paid for a student living with you, sponsored by a qualified organization
Out-of-pocket expenses when you serve a qualified organization as a volunteer
On page 2:
You can deduct your contributions only if you make them to a qualified organization. Most organizations, other than churches and governments, must apply to the IRS to become a qualified organization.
How to check whether an organization can receive deductible charitable contributions. You can ask any organization whether it is a qualified organization, and most will be able to tell you. You also can check by going to IRS.gov/TEOS. This online tool will enable you to search for qualified organizations.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.