If Google's search records are anything to go by, more people visit this site looking for the little-used phrase 'carpe diem' than they do for any other phrase.
'Carpe diem' is usually translated from the Latin as 'seize the day'. However, the more pedantic of Latin scholars may very well seize you by the throat if you suggest that translation. 'Carpe' translates literally as 'pluck', with particular reference to the picking of fruit, so a more accurate rendition is 'enjoy the day, pluck the day when it is ripe'. The extended version of the phrase 'carpe diem, quam minimum credula postero' translates as 'Pluck the day, trusting as little as possible in the future'.
The meaning is similar to that of many proverbs that we continue to use in English and is a warning to make the most of the time we have, with the implication that our time on Earth is short. Other such proverbs are 'Strike while the iron is hot', 'The early bird catches the worm', 'Gather ye rosebuds while ye may', and so on.
The original source for the Latin phrase is the lyric poet Quintus Horatius Flaccus (65 BC – 8 BC), more widely known as Horace. The term is first found in Odes Book I:
Dum loquimur, fugerit invida
Aetas: carpe diem, quam minimum credula postero
which translates as:
While we're talking, envious time is fleeing: pluck the day, put no trust in the future
Many authors have quoted the Latin original, but it was Lord Byron's use of the phrase that first began to integrate it into English. He included it in his 1817 work 'Letters', which was published in 1830 by Thomas Moore:
"I never anticipate, - carpe diem - the past at least is one's own, which is one reason for making sure of the present."
The noble George Gordon Noel, sixth Baron Byron, is better known as a womaniser than as a Latin scholar, but he was well versed in the language and was a Horace aficionado. He was taught Latin as a child by the son of his bootmaker and went on to write his version of Horace's Ars Poetica (The Art of Poetry), as 'Hints from Horace', in 1811.
See also - Latin Phrases in English.