A resume - sometimes called a 'Curriculum Vitae' or 'CV' - is a summary of your skills, education and work experience. A good resume demonstrates how your skills and abilities match up with the requirements of a job.
How long should a resume be?
Resumes give you the opportunity to sell yourself to a potential employer. A resume is not an exhaustive list - if it's too long it probably won't get read at all. The best resumes are usually no longer than one or two pages.
Do I need to change my resume every time?
You should change your resume with every job application so that it lists the skills and experiences you have that are most relevant to the job you're applying for. A tailored resume will be much more successful than a generic one, even though it means more preparation.