Having over 12 years of keyboarding experience I’ve played on numerous boards and have come to realize the various differences and nuances between the types. There are formal definitions out there and this list is probably not exhaustive, but it reflects my personal opinion. If you are reading this and are unfamiliar with keyboards this is a good place to start.

Midi controllers: Make no sounds on their own. Plug them into another device such as a keyboard or laptop to generate sounds.

Synthesizers: Are single focused purely on electric/digital sounds and manipulating those signals into new sounds. These are typically used for electronic genres, backing loops, bass, and lead parts.

Organs: While they are technically probably considered synthesizers, these keyboards are dedicated to reproducing organ sounds as realistically as possible.

Arrangers: More advanced with a “brain.” They usually contain multiple sounds such as Piano, Organ, Pads, Synths, and/or other samples. They can allow the player to become a “one man band.”

Workstations: These are like arrangers + more sounds and more capabilities such as editing, sampling, multiple effect chains, setting up songs/programs, etc. They are generally larger and more expensive than arrangers.

Digital/Electric/Stage Pianos: As close to a real piano as you can get in electronic form. Some of these come with a couple of sounds such as organ, pads, or strings.

Personal/Portable Generic Keyboards: Stuff like the Casios and Yamahas you’ll find at Wal-Mart and the cheaper ones at Guitar Center. While these do fall into the other categories they are entry level and generally not as full featured or high quality.

Some of the above categories are blended on certain boards. Many are considered arranger/workstations, and some boards can also double as midi controllers, etc. There are also apps, devices dedicated to beats, vintage/real hardware, and more. The differences also extend way beyond what I wrote but, like I said, this is just a starting point.