The heliopause is the theoretical boundary that marks the end of the influence of the Sun's solar wind and the beginning of interstellar space. It is the outermost edge of the heliosphere, which is the region of space dominated by the Sun's influence. The heliopause is thought to be a complex and dynamic region where the solar wind slows down and the pressure of the interstellar medium becomes dominant. It is an important boundary in understanding the interactions between our solar system and the surrounding interstellar space. Scientists study the heliopause to learn more about the structure and behavior of the heliosphere and the dynamics of the interstellar medium.