MRC is a file format that has become an industry standard in cryo-electron microscopy (cryoEM) and electron tomography (ET), where the result of the technique is a three-dimensional grid of voxels each with a value corresponding to electron density or electric potential.
MRC files are used to store data from cryo-electron microscopy (cryoEM) and electron tomography (ET), which both produce 3D grids of voxels representing electron density or electric potential.