In policy debate, a drop refers to an argument which was not answered by the opposing team. Normally, a "dropped" or conceded argument is considered "true" for the purposes of evaluating a debate.
"Silence is compliance." (Sometimes, "Silence is consent.") Debaters tend to use this as a general rule while evaluating a debate round. If a team says nothing against an argument, then because 'silence is compliance', they must agree to whatever the argument was.
An argument is normally considered dropped if it is not answered in the speech in which the opposing team has the first opportunity to answer it. Generally, in the first affirmative rebuttal, the speaker is required to answer all arguments made so far by the negative team. This is because if the affirmative chooses to respond to the arguments in the second affirmative rebuttal, it is abusive to the negative because the affirmative gets the last speech, leaving the neg with no way to refute any argument made.
Many debaters refer to dropped arguments as "conceded," "unanswered," or "unrefuted."
Some judges will not evaluate some arguments, even when they are dropped, such as arguments labeled "voting issues" but which are unsupported by warrants. For example, "the sky is blue, vote affirmative" is an argument that most judges would believe does not need to be answered.
Debaters constantly use the "dropped egg" argument to refer to arguments dropped by the opposing team, stating that "A dropped argument is like a dropped egg. Once an egg is dropped, it can not be fixed (or whole) again. Therefore, you should disregard their argument..." etc. This argument is optimal for lay, or parent, judges who need a reference to real life to understand the multiple (sometimes complex) arguments of policy debate.