The word for a second-year student in high school or college is “sophomore.” In the United States, a high-school sophomore is usually in 10th grade, while a college sophomore is in the second year of an undergraduate program.
The term belongs to the familiar American sequence “freshman, sophomore, junior, senior.” It is most strongly associated with U.S. education; in Britain, Canada, Australia, and many other English-speaking settings, students are more often called “second-year students.”
“Sophomore” is also used beyond classrooms. A professional athlete in a second season, a television program in its second season, or an artist releasing a second major album may be described as a sophomore. The related phrase “sophomore slump” refers to a disappointing second effort after a successful first one.
The word is traditionally explained as combining Greek roots associated with “wise” and “foolish,” producing the idea of a “wise fool.” That explanation is widely repeated, although the word’s exact historical development is more complicated. A sophomore is also an underclassman, along with a freshman; juniors and seniors are upperclassmen.