What is the idea/concept behind the expression carpe diem?
Carpe diem is a phrase taken from the Latin used by the poet Horace. The entire phrase is Carpe diem quam minimum credula postero, "Seize the day, trusting as little as possible to the future." One should make the most of the present and not trust in the future; time is fleeting and nothing is certain.
The idea of making the most of the present is found continually in philosophies, religions--such as the Rabbinic phrase "And if not now, when?"--and, of course, poetry and other literary genres.
In the film "The Dead Poet's Society," the teacher at an exclusive boys' school tells his students, "Carpe Diem," teaching them the meaning of this phrase in his course and through his activities with them on campus. He tells his students "We are food for worms," and as the poet Robert Herrick, writes, "Gather ye rosebuds as ye may." Mr. Keating shows the boys photos of former students who are now dead, impressing upon them the importance of learning all they can in the present time so that they will have rewarding lives.