A resume is the representation of your professional self. It is a concise compilation of your educational and professional experience, as well as the skills that make you desirable for the workforce. It is what you use to sell your merit and skills to potential employers.
For example, if you took a job and only stayed there for a month or so, you wouldn’t want to include that position. If you’ve been out of college for more than five years, it’s generally best to remove any internships you’ve had, assuming you have other professional work experience to fill the gap.