What does the abbreviation CDF stand for? 

CDF can stand for multiple things, but some of the common meanings include:

1. Cumulative Distribution Function: In mathematics and statistics, the cumulative distribution function (CDF) is a function that gives the probability that a random variable is less than or equal to a certain value.

2. Children's Defense Fund: The Children's Defense Fund (CDF) is a nonprofit organization focused on child advocacy and welfare.

3. Central Depository Fund: A Central Depository Fund (CDF) is a financial institution that holds and manages securities on behalf of investors.

4. Common Data Format: Common Data Format (CDF) is a file format used for storing and sharing scientific data.

5. Collective Defensive Fire: In military terminology, Collective Defensive Fire (CDF) refers to coordinated defensive fire by a group or unit against enemy threats.

It's important to note that the meaning of CDF can vary depending on the context.