GIL Grade MC3D is a specific lingo used in the PCB industry to describe a composite laminate material. This laminate is comprised of woven glass surface sheets that are present on both sides of a glass paper core. The unique composition of GIL Grade MC3D results in its excellent electrical properties, particularly its low and stable dielectric constant (Dk) and dissipation factor (Df). These electrical characteristics make GIL Grade MC3D a highly desirable material for applications requiring high-performance and reliable circuit boards. While no further information is provided in the given context, it can be inferred that GIL Grade MC3D is commonly used in the manufacturing of printed circuit boards to ensure optimal electrical performance.