What is a coverage type
The definition of a coverage type is:
The method to derive test situations from the test basis
A coverage type is aimed at acheiving a specific coverage to descover a specific kind of errors. (Think of interface errors, input validation errors, data processing errors). This way the different errors are detected more effectively then by specifying ad hoc test cases. A coverage type A can only be called "better" then a different coverage type B if at least all errors detected by B are also detected by A - in addition to A detecting even more errors.