The Monochrome Display Adapter was the earliest display card in use in PC-style computers. If I recall correctly, it supported an 80x25 grid of characters that could be bright, regular, dim, blinking, or underlined. It was not a "video" card or "graphics" card; it only supported a single character mode. Now it is virtually extinct and modern cards, crufty as they are, do not support the original MDA graphics mode if I recall correctly.

MDA was quickly superceded by the superior Hercules adaptor, which supported both the MDA text mode as well as a decently high-resolution monochrome graphics mode.