The phrase is understood as an appeal to live life in pleasure, without postponing all the entertainment for the future, which may not come. Carpe diem is kind of the opposite of memento mori. If the latter calls to remember the end, then the former calls not to forget the present.
This phrase is often used as an excuse for taking unexpected action and making the most of life's opportunities. No one knows if tomorrow will come, so today you need to act to the maximum.
Where does Carpe Diem come from?
The term "carpe diem" is attributed to the eminent Roman poet Quintus Horatius Flaccus (known primarily as Horace), who mentions this concept in his collection of poems known as the Odes:
"Do not inquire (we are not allowed to know) what end the gods have assigned to you and what to me, Leuconoe, and do not waste your time with Babylonian horoscopes.
How much better is it to bear with patience whatever shall happen!
Whether Jupiter have granted us more winters, or this is the last one, which now breaks the Etruscan waves against the opposing rocks, be wise, and strain the wine, since time is short, limit that far-reaching hope.
While we’re talking, envious time is flying:
seize the day, place in tomorrow as little trust as you can [carpe diem, quam minimum credula postero]."
— From Horace's "Odes" (Book I, Poem 11), circa 23 BCE. The English translation that appears here represents a combination of a number of translations, and was edited for clarity.
Important moments of existence are often reflected in literary or colloquial language. Popular expressions or phraseological units are an example of this. More often they are created on the basis of what worries people or what areas cause controversy. Death and life are no exception.