Rex Block
Sources: Various internet sites
A Rex Block is when a high pressure system sets up north of a low pressure system. This prevents weather systems from moving through and forces them to go around the Rex Block. This results in relatively quiet weather for areas east of the Rex Block
Very often both the high and the low are closed, meaning that the isobars (or constant geopotential height lines) defining the high-low close to form a circle.
Rex blocks are named after meteorologist Daniel F. Rex, who first identified them in 1950.