You can design different mold types, depending upon whether you want to produce a single part or multiple parts from a single mold.
Before designing the mold, including the runner system and cooling system, you should analyze the part to ensure that it's design is suitable. You will then determine whether you are designing a mold for a single part, which is a single cavity mold, or for multiple parts, which is a multi-cavity mold. Multi-cavity molds are used for multiple iterations of the same part, or for multiple parts of the same design, for example, the top and bottom of a remote control in a family mold.