What do we mean by CAM (a special photosynthetic pathway) in desert plants?

Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway present in some plants such as desert plants. These plants fix carbon dioxide during the night, storing it as the four-carbon acid, malate. The malate is then reduced to a three carbon compound oxaloacetic acid and the CO2 is released during the day, where it is concentrated around the enzyme RuBisCO, thus increasing the efficiency of photosynthesis.

 The CAM pathway allows stomata to remain shut during the day, reducing transpiration; therefore, it is especially common in plants adapted to arid conditions.