I believe it meant in both life and philosophy, and in other ways.

World War One brought about changes in states; it saw the state intervene in people's lives, through things like healthcare and employment, interventions that would have been unthinkable in classical liberal ideology. It provided the breeding ground for new political ideologies, Communism and Fascism, and launched new forms of Art, which championed the Avant-Garde, like Impressionism and Dadaism. Motion Pictures and mass media like newspapers were instrumental in mobilizing populations during the war, and became staples of post-war 'mass culture'. It lead to huge developments in aviation, that propelled aircraft towards their eminent positions in both civil and military uses, while also spurring greater development in the field of automobiles. The developments, innovations, and changes wrought by the 'Great War', left a massive imprint on the rest of subsequent history.

Essentially, it also does also mean the modern era. British Marxist Historian the late Eric Hobsbawn, championed the concept of a 'Long 19th Century', which began in 1789, and ended in 1914, leading to the 'short twentieth century', from 1914 to 1991.

David Stevenson, "1914-1918" David Reynolds, "The Long Shadow" Paul Fussel, "The Great War and Modern Memory"