The first definition of piety that Euthyphro provides is a definition by example, or an ostensive definition. He says that what is pious is what he is doing (prosecuting the wrongdoer) (5d). Socrates rejects this definition because it is the wrong kind of definition. Socrates wants a conceptual definition. A conceptual definition of a term provides a set of criteria that when met, the term is applied correctly. In other words, a conceptual definition gives a set of conditions that need to be fulfilled in order to use the word accurately. Contrast these two definitions for 'governor':
Ostensive definition: Jerry Brown is the governor.
Conceptual definition: The governor is the top political leader in the state in the executive branch of government.
In the first case, an example is provided, but we don't have any general knowledge or information about what a governor is. In the second case, we get some abstract and general information about what a governor is.
Socrates is concerned not just with finding examples of piety; he also wants to identify the abstract form, or the general conditions that define piety.