The term lacrimation means "the secretion of tears especially when abnormal or excessive"1.
Animals do not tear up or cry for emotional reasons as humans do. If you see that your pet has excessive tearing by the eyes, this is something to address right away. Things happen quickly with eyes, and tearing can be an indicator of irritation, inflammation, injury or infection to the eye (or surrounding tissue) and should be examined by your veterinarian as soon as possible.
Possible causes of lacrimation in pets include, but are not limited to: allergy, physical or chemical irritant (misplaced eyelashes, eyelid growth, chemical spill), wound or direct injury (clawed in face), corneal ulcer, blocked tear ducts, some systemic diseases (such as pseudorabies), or toxin ingestion.
It is important to note that some light colored dogs may develop "tear staining" on the fur on the inside corner of the eye. This is usually caused by excessive tearing (lacrimation), and this chronically wet area is an idea environment for bacteria and yeast. It is the growth of these microbes that causes the reddish brown "stain" on the hair coat. Please see your veterinarian to diagnose the underlying cause of lacrimation.
Epiphora: "Watering of the eyes due to a blockage of the lacrimal ducts or the excessive secretion of tears." (source: Dictionary.com