The "math" section of the GMAT (Graduate Management Admissions Test) is officially known as the Quantitative section. It consists of 37 multiple-choice questions covering both Problem Solving and Data Sufficiency.
Problem Solving questions are mostly word problems. They test your ability to solve mathematical problems involving arithmetic, algebra, and geometry and word problems by using problem-solving insight, logic, and applications of basic skills.
The basic skills necessary to do well on this section include high school arithmetic, algebra, and intuitive geometry — no formal trigonometry or calculus is necessary. The exam tests these skills as well as logical insight into problem-solving situations.
Occasionally, questions refer to a graph, chart, or table, so you should understand and know how to derive information from them.
Data Sufficiency questions don't necessarily require you to calculate a specific mathematical answer. You must decide if the data given in the statements is sufficient to answer the question. This section tests your ability to analyze a problem; to recognize relevant or irrelevant information in determining the solution of that problem; and to determine when you have sufficient information to solve that problem. You use the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in July or the meaning of counterclockwise).
Correctly answering these questions requires competence in high school arithmetic, algebra, and intuitive geometry. You also need mathematical insight and problem-solving skills. No advanced mathematics is required.