Final answer:
In a DBMS, defining data pertains to specifying the data types for various database fields to ensure appropriate and efficient storage and data manipulation.
Step-by-step explanation:
When defining data within a DBMS (Database Management System), we are interested in c. Data types. This is because data types determine the kind of data that can be stored in a database field, such as integers, decimals, text, and dates, among others. The choice of data types affects how data can be manipulated and stored efficiently within the database. It is not related to physical concepts like velocity, acceleration, or energy.