Granularity
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Granularity is the extent to which a system contains discrete components of ever-smaller size. An example of increasing granularity: a list of nations in the United Nations, a list of all states/provinces in those nations, a list of all counties in those states, and so on until you have a list of all people in the countries that belong to the U.N.
In computing
In parallel computing, granularity means the amount of computation in relation to communication, i.e., the ratio of computation to the amount of communication.
"Fine-grain parallelism" means individual tasks are relatively small in terms of code size and execution time, "coarse grain" is the opposite.
The smaller the granularity, the greater the potential for parallelism and hence speed-up but the greater the overheads of synchronisation and communication. (The last two paragraphs are from FOLDOC (http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?granularity).)