In the introduction to K&R there is the following text:
Similarly, C offers only straightforward, single-thread control flow: tests, loops, grouping, and subprograms, but not multiprogramming, parallel operations, synchronization, or coroutines.
grouping refer to? It is not in the index, and searches have been unfruitful so far. I've programmed some C (though I'm far from an expert), and haven't heard the term before.