The term "algebra" has its roots in the Arabic word "al-jabr," which means "completion" or "restitution." It was first used by the mathematician al-Khwarizmi, who wrote a book called "Al-Jabr wa'l-Muqabilah" (Translation: "The Composition of Algebra and Balancing"). In this book, al-Khwarizmi introduced the concept of solving linear equations using symbols to represent unknowns.
Over time, the term "algebra" came to be used more broadly to refer to a branch of mathematics that deals with the study of relationships between variables, including algebraic expressions and equations, polynomials, matrices, and functions. In essence, algebra is concerned with finding patterns and expressing them in mathematical terms, using symbols and formulas to represent and solve problems involving those patterns.