Nozzle Check
A test pattern printed to confirm that every ink channel is firing correctly.
In depth
Inkjet nozzles clog when ink dries in them, and a single blocked nozzle produces a fine banded line running the length of every print. Because the fault is easy to miss on a busy image and obvious on a test pattern, running a nozzle check before an important print is standard practice.
Examples in practice
A gap in the light cyan block of a nozzle check explains the faint line running across an otherwise perfect sky.