There are still plenty of MDs in the world, but these days it's mostly used in finance and consulting to represent the first layer of leadership below the c-suite.
It can vary, though; e.g. Kevin Sneader is the de facto CEO of McKinsey, but his official title is Global Managing Partner and his predecessor used Managing Director.
It can vary, though; e.g. Kevin Sneader is the de facto CEO of McKinsey, but his official title is Global Managing Partner and his predecessor used Managing Director.