What is the difference between graphic design and visual communication? Which one is good to learn and popular?

There is no difference between graphic design and visual communication.

Graphic design, also known as visual communication design, is the use of "vision" as a means of communication and expression, through a variety of ways to create and combine symbols, pictures and text, which are used to make visual representations to convey ideas or messages. Graphic designers may use specialized skills in typography, visual arts, page layout, and computer software to achieve the purpose of a creative project. Graphic design can often refer to the process involved in making (designing), as well as the finalized work.

Common uses of graphic design include logos (trademarks and branding), publications (magazines, newspapers, and books), print advertisements, posters, billboards, website graphic elements, signs, and product packaging. For example, product packaging may include logos or other artwork, choreographed text, and pure design elements such as stylized images, shapes, sizes, and colors. Combination is one of the most important characteristics of graphic design, especially when the product uses pre-existing materials or a blend of multiple elements.