$64,000 ques·tion, the /ˌsɪkstifɔː ˌθaʊz ə nd ˌdɒlə ˈkwestʃ ə n $ -fɔːr-, -ˌdɑːlər-/ BrE AmE noun
the most important thing that people want to know about something:
The $64,000 question is whether or not the rocket will take off safely.
$64,000 ques·tion, the /ˌsɪkstifɔː ˌθaʊz ə nd ˌdɒlə ˈkwestʃ ə n $ -fɔːr-, -ˌdɑːlər-/ BrE AmE noun
the most important thing that people want to know about something:
The $64,000 question is whether or not the rocket will take off safely.
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012