When working with any manufacturing process, a number of defects unique to that process commonly occur. This is true across many processes and industries, including plastic injection molding and high volume injection molding.
Delamination, when a finished part has a layer of flaky material at the surface, hurts both aesthetic of your part and its strength. Caused by moisture contamination of the resin pellets or by other contamination of the melted resin with a dissimilar resin, or by release agents in the mold, delamination is the result of the resin being prevented from bonding.
Discoloration is simply when a finished part is a color different than intended
Burn marks are surface marks, sometimes advancing to degraded plastic, that are caused by either trapped air which becomes overheated or actual resin that overheats.
Flow marks are lined patterns, often wavy, or discoloration on a part surface. They are most commonly caused by resin cooling too quickly or improper gate location.
Sometimes known as burrs, flash is the occurrence of thin, wafer-like protrusions on a finished part caused when melted resin escapes the mold cavity.
A short shot is literally when a shot of resin falls short of filling the mold. It can be caused by attempting to use the wrong resin type or by poor process settings, but is most commonly caused by gate blockages or too small of a gate diameter, a common problem due to too low pressure or not enough heat.