Picking the Perfect Pair: A Pants Primer
Before I get in too deep with the jargon of pants it’s important to point out how fluid these terms are. Despite what we might read here or anywhere else, expect to see some of these terms used interchangeably elsewhere. I think of pants as the catch-all term, while slacks tends to include trousers, chinos, and khakis. Of course parts of the UK say pants instead of underwear and for some people, slacks are only for women.
Trousers
Trousers are your nice pants. They can either be paired with a suit or sold alone. Modern trousers were made fashionable by Beau Brummell, the original Dandy, in the early 19th century. Brummell believed, and most writers today agree, that trousers look best when they’re tailored.
http://www.realmenrealstyle.com/mens-trousers-style-fit-fabric/