In an interesting case study of the dangers of making an ambiguous bet, on Longbets Martin Rees bet Steven Pinker that,

A bioterror or bioerror will lead to one million casualties in a single event within a six month period starting no later than Dec 31 02020.

Given the ambiguity of what "bioerror" means, some have speculated in the comment section that the current coronavirus pandemic should qualify. Rees had specified that,

By "bioerror", I mean something which has the same effect as a terror attack, but rises from inadvertance rather than evil intent.

and Longbets clarified,

Casualties will be defined by WHO, CDC, or BPHS, whoever has the highest numbers. Casualties should ideally include "victims requiring hospitalization" and not include indirect deaths caused by the pathogen, although ultimately Long Now will rely on the criteria set by the above organizations for determining casualties to adjudicate this bet.

Pinker was worried about the resolution criteria,

We'd need definitions of "casualty" (death, permanent disability, or just infection?), "bioterror" (state-sponsored? apolitical vengeance/spree killing?) and "bioerror" (I assume a mere lack of preparedness doesn't count). But that shouldn't be too hard.

Unfortunately, it's not clear that Pinker's worries were addressed. The procedure for resolving bets is outlined here.

How will the Longbets "bioerror" question resolve?

If Longbets declares Martin Rees the winner of the bet, then this question resolves positively. If Steven Pinker is resolved the winner of the bet, then this question resolves negatively. Otherwise, it resolves ambiguously.