"Electronic drum" can refer to the true electronic drum, which is the drum's answer to the electric guitar. It can also refer to a device that plays a programmed drum beat for musicians to play with and keep time. There are also electronic drum programs, sometimes called digital drums, that are designed for use on the computer.
Drum effects also can be ambiguous for the neophyte. They refer to either a device that alters the electronic drum sound, or the altered sound itself. While there is an infinite number of altered sounds that can be produced, some of them more common than others, the devices that make them are quite basic. Many of them even let you create your own specialized sound effects.
Effects included "inside" a device are considered to be "on-board." These effects are often accessed by flipping a switch, pressing a combination of buttons, or by turning a dial. On-board effects are generally permanent fixtures in the electronic drum, drum device, or program, but some more expensive models allow users to customize and change on-board effects to suit their style. On-board effects can often be used in tandem with other effects devices to create a series of effects to further personalize sound.
External effects are produced by devices that plug into the output of your electronic drum or drum machine, and into the input of your amplifier. These devices usually come equipped with pedals, dials or buttons that you can use to modify the sound. The biggest advantage of an external effects device is the freedom to modify your sound to perfection. You can also hook your external effects devices into a series, piling effect upon effect to create a truly massive sound.
Plug-in effects are programs designed to work with digital drum programs on your computer. Some of the more advanced digital drum sets and devices also support plug-ins. Plug-in effects are generally designed to simulate the look and feel of the physical external effects devices. For this reason, they usually have an on-screen control board separate from the programs they "plug-in" to that allows users to modify the effects without having to rely on the "host" program. Plug-ins usually require another program to run, and are typically made to work with most standard music creation programs.