生物にとって、冬は直接に命の危険にさらされる季節である。それにつれて生物は活動を控えたり、様々な方法で冬眠や越冬に入る。落葉樹は葉を落とし、宿根草は地上部を枯らす。人間は防寒を主目的とした冬服に着替え、さらに襟巻きなどの防寒具を着用するが、霜焼け・凍傷を起こす事や凍死する者もいる。暖房器具を使用するのも冬のことであり、こたつやストーブに体を寄せる楽しみもあるが、それに起因する一酸化炭素中毒も冬に度々発生している。
冬という季節が生まれるのは、太陽高度の差によって気温が変わることが大きな原因である。地球が地軸を傾けて公転しているために、同じ地点でも季節により太陽高度が変わり、太陽高度が低くなると冬になる。赤道に近い低緯度地域では、季節による太陽高度の差が小さいので冬に目立った気象の変化はない。また、極地や高緯度地域では冬に太陽が昇らない極夜という現象が起こる。また、その土地の標高や気団、海流、風などが冬の気候に影響を与えるため、同じ緯度にあっても冬の気候に差が出る。例えば、北緯43°付近にあるモナコでは1月の最低気温は8℃前後だが、同じ緯度にある旭川では同じ月に-14℃前後まで下がる。日本では秋から次第に寒くなり、やがて野外で霜や雪など氷に関わる現象が見られるのが冬である。また、冬至までは昼間の時間は短くなり、夜が長くなる。シベリア高気圧が張り出し、西高東低の気圧配置になると、これを冬型の気圧配置といって、北西の季節風（北風）が強く吹き、日本海側では雪、太平洋側では空気が乾燥して晴れとなる。寒さが弱い冬を暖冬（だんとう）という。反対に、寒さが厳しい冬・寒さが強い冬を、厳冬（げんとう）や寒冬と言う。
冬（ふゆ）は、四季の一つであり、一年の中で最も寒い期間・季節を指す。秋と春にはさまれた季節。二十四節気や旧暦のように、一年中で最も太陽の高度が低く夜が長い期間を指すこともある。北半球では冬至後の1月-2月頃に気温が低いことが多く、南半球では夏至後の7月‐8月頃にあたる。日本の気象庁では一日の日最低気温が0℃以下の日を冬日（ふゆび）、また、日最高気温が0℃以下の日を真冬日（まふゆび）と呼んでいる。このような日は1月を中心に前後の毎年12月から翌年3月頃にかけて発生するから（ただし、年や地域によっては、11月・4月でも生じる場合もある）、この時期のあたりが冬の範囲に入る。冬が特別・特有とされる物（特に収穫物）に付いては旬#冬を参照。
登場する国、生物はすべて架空のものである。登場人物の台詞より、過去に第三次世界大戦とも称される大規模な戦争があり、その後に氷河期を迎えているらしい。フィオナ一行が旅する時代は生命が溢れており、氷河期を終えた後の時代と推測される。
In October 2008, the Orange County Register's OC Political Pulse poll found that a third of responding Republicans believed that Obama had been born outside the United States. As a result of the widespread publicity given to the citizenship controversy, 60% of respondents in an Ohio State University survey carried out in November 2008 had heard of the issue. However, only 10% believed the claims that Obama was not a citizen.An opinion poll carried out for Daily Kos by Research 2000 in July 2009 found that 77% of Americans believed that Obama was born in the U.S., while 11% didn't, and 12% were unsure. However, Republicans and Southerners were far more likely than other political or demographic groups to doubt that Obama was born in the United States. 58% of Republicans either believed that Obama was not born in the U.S. (28%) or were not sure (30%), with 42% believing that he was. An overwhelming majority of Democrats (93%) and independents (83%) believed that he was born in the U.S. Support for the belief that Obama was born outside the U.S. was strongest in the South, where only 47% of those polled believed he was born in the U.S., compared with an average of 90% of residents of the Northeast, Midwest and West. A marked racial disparity in the South was also apparent. The Politico's congressional reporter, Glenn Thrush, commented that the Research 2000 poll "explains why Republicans, including Roy Blunt, are playing footsie with the Birther fringe". Writing on National Journal's Pollster.com blog, Brendan Nyhan observed that the poll "suggests that the encouragement of the birth certificate myth by conservative pundits and Republican politicians has begun to activate the GOP base on this issue".A Public Policy Polling survey carried out in August 2009 found that only 32% of Republicans in Virginia thought that Obama was born in the U.S., 41% thought he was foreign-born and the remaining 27% were unsure. In Utah, an August 2009 poll carried out for the Deseret News and KSL-TV found that 67% of Utahns accepted the evidence that Obama was born in the U.S. The poll found that those who do not believe that Obama was born in the United States, or do not know, are predominantly middle-aged, lower-income Republican-leaning individuals without a college education.A Pew Research Center poll found that 80% of Americans had heard about the Obama citizenship claims by August 2009. The poll found a significant partisan divide in views of the news coverage, with 58% of Democrats saying that the allegations had received too much attention from the media. Republicans were more inclined to say that the allegations had received too little attention, with 39% expressing this view against only 26% saying that the controversy had received too much attention.In a Harris Poll online survey of 2,320 adults conducted in March 2010, 25% of the respondents said they believed that Obama was "not born in the United States and so is not eligible to be president". In a July 2010 CNN poll of adult Americans, 16% said had doubts that Obama was born in the United States, and a further 11% were certain that he was not.