1. A person who has successfully completed a course of study: This is the most common meaning. It refers to someone who has earned a degree or diploma from a college, university, or other educational institution, such as a high school graduate, a college graduate, or a postgraduate (graduate school) graduate.
2. The act of completing a course of study: This refers to the process itself – *to graduate* means to successfully finish your studies and receive your degree. For example, "She graduated from Harvard last year."
In short, "graduate" can be a noun (a person who has graduated) or a verb (the act of graduating).