Undercut In Plastic Injection Molded Part Design 

Undercuts are those features in an injection-molded part that prevent its ejection from the mold.

Draft Angle In Plastic Injection Molded Part Design 

A draft angle refers to that slant applied to the sides of most features of injection molded parts. Positioning of the injection angles is such that they run towards the direction of the mold’s pull and parting line. They help to release the molded parts from the mold easily.

99% of your injection molding design will require draft angle injection molding for a successfully made part. The angle tapers on the molded part's surfaces. Therefore, the part can easily slide across the mold's cavities and cores as you're demolding. 

Shutoff In Plastic Injection Molded Part Design 

Shut-Off angle is applied for prevent the mold parts (Core and Cavity) from crashing into one another if there is any slight misalignment upon mold parts closing.

Shut-OFF angle also prevent galling that would occur if vertical metal faces were rubbing against each other.