Simultaneous equations refer to a set of equations that need to be solved simultaneously. This means that the solutions to all the equations must satisfy all the equations at the same time. They can also be called a system of equations or a set of linear equations. Additionally, they are defined as a group of two or more equations that involve the same variables. They are commonly used in mathematics, physics, engineering, and other fields that require solving complex mathematical equations. It is important to note that simultaneous equations can come in different forms, including linear and non-linear equations, and they can have different types of solutions.