In the United States, "resume" and "CV" are often used interchangeably, but they can mean different things. In other countries, the difference is clearer.
Resume (U.S.)
A resume is usually 1–2 pages. It summarizes your experience, education, and skills for a specific role. It is tailored to the job and focuses on the most relevant information. This is the standard document for most U.S. job applications.
CV (Curriculum Vitae)
In the U.S., a CV is often a longer, more detailed document used in academia, research, or medicine. It includes full publication lists, grants, teaching experience, and detailed education. It can be many pages. In the U.K. and some other countries, "CV" is the standard term for what Americans call a resume (1–2 pages).
Which to Use
In the U.S., use a resume (1–2 pages) for most jobs. Use a CV when the employer or field explicitly asks for one (e.g., academic, research, medical). When applying abroad, check local norms—in the U.K., "CV" usually means a 1–2 page document similar to a U.S. resume.
Summary
Resume: short, tailored, 1–2 pages. CV: longer, detailed, used in academia/research/medicine in the U.S., or the standard word for "resume" in some other countries.