In general, a liability is an obligation between one party and another not yet completed or paid for. In the world of accounting, a financial liability is also an obligation but is more defined by previous business transactions, events, sales, exchange of assets or services, or anything that would provide economic benefit at a later date. They can include a future service owed to others (short- or long-term borrowing from banks, individuals, or other entities) or a previous transaction that has created an unsettled obligation.
Generally, liability refers to the state of being responsible for something, and this term can refer to any money or service owed to another party. Tax liability, for example, can refer to the property taxes that a homeowner owes to the municipal government or the income tax he owes to the federal government. When a retailer collects sales tax from a customer, they have a sales tax liability on their books until they remit those funds to the county/city/state.