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 exploration of the chiasmal and retrochiasmal visual pathways is based on magnetic resonance imaging. A bitemporal hemianopsis should suggest a lesion of the optic chiasm while a homonymous lateral hemianopsis should lead to a search for a lesion of the retrochiasmal visual pathways.