The legal authority of a court to try cases and rule on legal matters within a particular geographic area and/or over certain types of legal cases.
Jurisdiction is very important for the practical enforceability of legal rights, for example contractual rights.
Similar legitimate rights enjoyed by law enforcement agencies, for example the police of a particular state.
The geographical or other area which is subject to a particular legal system or the authority of its law enforcement agencies, or more usually both.
For example, a country.
In relation to tax, a geographical or other area which is subject to a particular tax system or its tax authorities, or both.
For example, a country or a state, or indeed any authority which has legitimate powers to levy tax.