Lebensraum was the term hitler used that meant
a. a dream of german domination of all europe.
b. a dream of german domination of the soviet union.
c. more power for germany over italy.
d. more living space for the germans.

Lebensraum was the term Hitler used that meant territorial development in Germany, or increase in territory. The definition can also be seen as just living space. 

Out of your options, D) more living space for the Germans makes the most sense, considering that it means the Germans were expanding their territory for more living space, just as the definition states.