Taxability may refer to the eligibility of a person or entity for taxation:

Taxable estate (Russian Empire)
Taxable REIT subsidiariesIt may also refer to the base upon which a tax system imposes a tax:

Taxable incomeTaxable wages
Taxable profitTaxable estate under an estate tax regime
Taxable real-estate under a property tax regime
Taxable goods and services under a sales tax regime
Taxable transactions under a transfer tax regime