Granularity

In 'Parallel computing', Granularity can be defined as a qualitative assess of the ratio of computation to communication.

1) Coarse Granularity- relatively huge amount of computational work is done among communication events. 

2) Fine Granularity- relatively little amount of computational work is done between communication events.

3) Observed Speedup- Observed speedup of a code, which has been parallelized, is termed as:

(Wall-clock time of serial) / (wall-clock time of parallel)

Granularity is one of the simplest and most extensively used indicators for parallel program's performance.