(histology) the use of a dye to color specimens for microscopic study
"The pathologist carefully applied staining to the tissue slide before placing it under the microscope to identify the cancer cells."
the act of spotting or staining something
"The fresh paint caused a terrible staining on the white walls that was impossible to remove."
present participle of stain
"The accidental spill left a permanent brown staining on his white shirt that wouldn't come out no matter how hard he scrubbed."