MKAD is a ring road encircling the city of Moscow.
The name is a transliteration of the Russian acronym МКАД. It's 109 km long. The average speed on the ring is 70-120 km/h (though some drivers tend to drive fast like manicas). Average waiting time is between 1 second and 5 minutes, though be aware of the many private taxi's stopping. Don't stop trucks, they are too slow anyway and stopping them might be difficult at most spots.
Hitchhiking around the ring is possible, though not every junction is good for hitching. When hitching the inner ring clockwise, it's not a good idea to use the intersections of the MKAD with Korovinskoe, Altufievskoe, Ostashkovskoe (Medvedkovo), Yaroslavl (M8), Kashirskij (M4) and the Warsaw (M2) highway.
Useable, but not very comfortable are the intersections at Novorizhkskoe (#9) and N. Leningrad (M10).
On the outer ring nearly all interchanges are useable.