Depending on the complexity of your part and whether or not features can be designed out of the part, the tool designer may need to add a side action. Side actions are special features that are designed into a mold to help achieve tricky part features. These add cost and increase mold complexity and maintenance.
Lifters release internal undercuts. Once the part has cooled, the lifter pushes up at an angle to release the undercut.
Slides release external undercuts. The part is molded around the features cut into the slide. Once cooled, the slide is pulled away from the part by an angled pin attached to the core side of the mold.