What is meaning of "peak oil"? and what is peak oil theory?

Question

What is meaning of "peak oil"? and what is peak oil theory?

Answer 1

Peak oil is the year our worldwide oil production (and use) will peak.  This future year, which we can only speculate on, keeps getting pushed further and further into the future as we continue to increase our oil reserves through exploration and recovery technology.

We are decades past the first estimates of 'peak oil'.

Answer 2

Hubbert's peak can refer to the peaking of production of a particular area, which has now been observed for many fields and regions. "Peak Oil" as a proper noun, or Hubbert's peak applied more generally, refers to a singular event in history: the peak of the entire planet's oil production. After Peak Oil, according to the Hubbert Peak Theory, the rate of oil production on Earth will enter a terminal decline. Based on his theory, in a paper[1] he presented to the American Petroleum Institute in 1956, Hubbert predicted that production of oil from conventional sources would peak in the continental United States around 1965-1970 (actual peak was 1970). Hubbert further predicted a worldwide peak at "about half a century" from publication and approximately 12 GB-yr in magnitude.

Half a century is 50 years. 1956+50= 2006. Hubbert's prediction of Peak Oil. The recent run up in oil prices is in part due to concerns that Hubbert was right.