Pants are clothing for the body above the ankles and below the waist, of one sort or another. The term is an abbreviation of pantaloons, a plurale tantum. However, it has two distinct meanings which vary between regions:
In American English, pants refers to a long outer garment worn over the hips and legs, which in British English are called trousers. The word is this sense is covered more completely at that article. In American English, "trousers" can either be synonymous with "pants" or have a more formal connotation. Therefore, all trousers are pants, but not vice-versa; jeans are pants but not trousers, while slacks (formal pants) are both. This definition is consistent with other languages such as the Spanish pantalones, which is contrasted with pantalones cortos (shorts, or literally "short pants").
In Britain, the term pants refers to undergarments known variously as underwear or underpants. It is a catch-all term that can denote anything from g-strings to boxer shorts, but all have the common feature that they are worn under trousers, skirts or pyjamas. The word "pants" has acquired humorous connotations in the last few decades, largely among younger people. Many stand-up comedians have used the word adjectively as a light pejorative term, especially when substituting other nouns in famous quotes or excerpts with the word "pants". In Japan, the word pantsu (パンツ) is a loanword from the English word "pants" and refers to underpants; however, it is worth noting that in some parts of Northern England the converse is true, i.e. pants refers to trousers.
Other uses
Also in the UK "pants" can be used as a slang word for something that is below par.
In Canadian drug use slang, "pants" can sometimes be a codeword for heroin.
Pants is considered by some an inherently funny word, e.g. the Spongebob Squarepants episode about ripped pants.
Clarence "Pants" Rowland was a former manager for Major League Baseball's Chicago White Sox, guiding them to the 1917 World Series title.
To "pants" someone (used interchangeably with "de-pants") colloquially means to pull a victim's pants down in public.
A UK rock band from Wickham, Hampshire, formed in 1996.
The British festival Green Belt gave birth to the informal and rebellious "worship your pants society" headed by persons sporting such titles as Dillon or Zebadee. It became famous for strange stunts that sometimes disrupted events at main stage. Some of the members made a giant "pants banner" that looked like an oversized pair of y-fronts.
In Britain "swinging your pants" is another term for dancing.
I think I want to travel with you, I'd no doubt have fun. 
