¿Qué es...? / ¿Cuál es...? (by Lazarus)
'¿Qué es tu nombre'? is a common mistake in Spanish, and the only way to answer this definition is by answering it as a definition, i.e. "My name is the word that I am known by". If you use '¿Qué..:? and the verb 'ser', these is how you should answer these questions:
What is your name? The Word that I am known by. What is your age? The period of time I have been alive. What is your height? The distance from the top of my head to the bottom of my feet. What is your job? The regular work which I normally do to earn money. What are the dimensions of the room? The distance between its walls.
¿Qué es tu nombre? La palabra con la que me conocen. ¿Qué es tu edad? El periodo de tiempo que llevo vivo. ¿Qué es tu altura? La distancia desde lo más alto de mi cabeza hasta mis pies. ¿Qué es tu trabajo? Lo que hago regularmente para ganar dinero. ¿Qué son las dimensiones de la habitación? La distancia entre sus paredes.
If you want a more 'normal? question, you shouldn't use '¿Qué''', but '¿Cuál''':
¿Cuál es tu nombre? Lazarus. ¿Cuál es tu edad? 35 ¿Cuál es tu altura? 1,80 ¿Cuál es tu trabajo? Profesor ¿Cuáles son las dimensiones de la habitación? 2 por 3 metros.
What is your name? Lazarus. What is your age? 35 What is your height? 1,80 What is your job? Teacher. What are the dimensions of the room? 2 by 3 metres.
As you can see, English works on common sense interpretations rather than on choice of words, but Spanish has a very precise mechanism here to determine whether one expects a definition, or simply information on a topic inquired. This mechanism, necessary or useless as it may seem, is a reality, and using it correctly is a must.
The same goes with other "qué" plus "ser" sentences:
Sé qué es tu nombre = I know what your name is (= I know the definition of "your name") Sé (cuál es) tu nombre = I know what your name is (= I know exactly what people call you)
Sé qué es tu edad = I know what your age is (= I know the definition of "your age") Sé (cuál es) tu edad = I know what your age is (= I know exactly how old you are)
