Socrates insists that Euthyphro begin to instruct him regarding what is holy and what is unholy. Socrates has Euthyphro agree with him that there must be one form or standard by which everything holy is holy and everything unholy, by contrast with the holy, is unholy. That is, all holy deeds must be holy by virtue of some feature or other that all holy deeds share in common. Socrates asks Euthyphro what this feature is.
Euthyphro suggests that prosecuting those who commit injustices is holy, and not prosecuting them is unholy. That one should prosecute those who commit injustices is holy is merely an example of a holy act, and not a definition of holiness itself. Euthyphro concedes that there are a great many holy deeds that do not consist in prosecuting a religious offender. Socrates then urges Euthyphro to give a more general definition and to identify a standard by which all holy deeds can be recognized as holy.
Euthyphro then goes on to posit a second definition: that holiness is what is agreeable to the gods. Euthyphro makes the distinction in making this claim between the definition of holiness as what is agreeable to the gods and the definition as what is approved of by all the gods. The main difference is that the second definition refers to "all the gods," whereas the first refers to "the gods." Euthyphro initially thinks holiness a simple matter of being what the gods like, but then Socrates points out that the gods often disagree. Some things that are agreeable to one god may be disagreeable to another. Thus, Euthyphro is forced to retreat to the position that only those things that all the gods agree upon and approve of can qualify as holy.
By asking for a general definition of what is holy, Socrates shows that Euthyphro has no understanding whatsoever.