3-to-6 months’ expenses, saved for emergencies.
An Emergence Fund is a fairly liquid chunk of assets (e.g. Savings Account) that can be called upon to cover you in the case of emergencies (car breaks down, AC goes out, break a leg). The size of your emergency fund is based on your Burn Rate.
Most sources I’ve read peg a good emergency fund goal at between 3 and 6 months’ living expenses. That is - enough to cover your absolute necessities. This is not necessarily equal to your burn rate, or even your Budget, but what those things could be reasonably brought down to without sacrificing too much. Basically you don’t need to include your monthly $200 donation to whatever charity in your emergency fund… just stop making that donation in the case of an emergency.