Plain English Meaning
A map used by air traffic controllers that shows the lowest altitude they can legally tell you to fly in each chunk of their airspace while giving you radar headings. It keeps you safely above terrain and obstacles in that area.
Full Definition
A controller's chart that depicts the minimum vectoring altitudes for each sector of a radar facility's airspace. Each sector shows the lowest altitude, in feet MSL, at which an air traffic controller may radar vector an IFR aircraft, providing required obstacle clearance (typically 1,000 feet over non- and 2,000 feet over designated mountainous terrain) within that sector.