Yes, billionaire is usually defined by networth, which consists of assets (whether liquid or not) minus liabilities (eg loans).
What you described below makes one a billionaire as long as the liabilities of the person, when deducted from the assets (properties) do not consume the assets.
If you have assets worth N5 billion, and liabilities (loans etc) worth N2 billion, your networth is N3 billion and you are still a billionaire.
But if you have assets worth N1.3 billion but owing N800m, that's networth of N500m. Still not a billionaire despite having assets of crossing a billion.
But in most cases, liabilities are usually not known, so assets (or equities) are usually used. Once you have assets or equities running into billions, you are a billionaire.