Liability is the opposite of asset. An asset is what you own and a liability is what you owe. Examples of liabilities are loans, rent, mortgages, interests, taxes, etcetera. Liabilities are often classified by their due date which is current and non-current liabilities. Current liabilities are liabilities that must be paid within the year whilst non-current liabilities are due after one year. 

Additionally, there is another special category of liabilities which is a contingent liability. Contingent liability is a possible liability that companies or corporations might face in the future such as lawsuits. Litigations are unforeseeable but assessing the outcome is probable and the amount of liability can be estimated reasonably. Those are the two variables to classify the liability as contingent liability.