Final answer:
The term 'Blank Check' refers to Germany's unconditional support to Austria-Hungary in 1914, leading to the outbreak of World War I.
Step-by-step explanation:
The 2-word term for freedom of action used of a 1914 message from Germany to Austria about attacking Serbia is Blank Check. This term refers to Germany's offer of unconditional support to Austria-Hungary in its confrontation with Serbia. After receiving this blank check, Austria-Hungary felt emboldened to declare war, which ultimately led to the outbreak of World War I as alliances and treaties pulled numerous countries into the conflict.