In the UK (where I'm from) we always say "CV". In the US, people normally say "resume" - although I believe in certain fields such as academia, "CV" is also used.
But in either case, it's a job-seeker's profile, listing essential information (contacts etc.,) employment and educational history, and other relevant information.
The format can be adapted to suit the applicant's situation (reverse chronological, functional, or a combination of the two) and often contains an objective or a skills summary at the top under the heading and contacts.
It gives great scope for highlighting relevant skills and experience to match the requirements of the position - so many savvy applicants don't just use the same resume over and over, but tailor each one to a specific job application.
They say that you only get a few seconds to grab a reader's interest - so it makes sense to put the most compelling information where it will best be noticed.