A cross fade is a dissolve from one video clip to another. There are two common cross-fades, a standard video dissolve and a filmic cross fade. In a standard video dissolve the transparency of the second clip is animated from zero to one hundred percent to create the fade effect.
In a filmic cross fade, the two images are inverted to simulate film negatives, then blended, with resulted being once again inverted to a final positive. This is closer to the fades created optically in the pre-digital era and many consider the result to have a warmer quality.