Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.
--------
Question: spintronics is a kind of electronics that uses the tiny magnetic fields that come from electrons as well as their electric charge.

Answer: spintronics

Question: a private prison is a prison run by a private company instead of the government.

Answer: private prison

Question: city designated by government ordinance (, seirei shitei toshi), also known as a designated city (, shitei toshi) or government ordinance city (, seirei shi), is a defined class or category of japanese cities.

Answer:
city designated by government ordinance