Code coverage means, how well your test set is covering your source code. i.e. to what extent is the source code covered by the set of Test cases. As mentioned in above answers, there are various coverage criteria, like paths, conditions, functions, statements, etc.
Chiasmus. Definition: Chiasmus is a specific type of parallelism. It consists of two parallel phrases in which corresponding words or phrases are placed in the opposite order.
The parallel involves expected congruence among similar components of the distribution of character states among organisms. The threefold parallelism is a manifestation of a world view based on linear hierarchies, whereas polarity determination is part of the methodology of phylogenetic systematics which assumes that organisms are grouped into a nested hierarchy.