Keyboard amplifiers are versatile speaker systems which accurately recreate the incredible range of frequencies keyed instruments produce. They need both a rounded low end like a bass amp, and a crisp high-end like a guitar amp. This means that they often include bass reflex ports and one or more tweeters to achieve a maximum span of frequencies.
Similarly, keyboard amplifiers tend to have very low distortion and a flat frequency response in both the upper and lower registers. They also often have multiple inputs, and in-built effects like reverb, compression, and equalisation, all of which make them perfect as compact, mono PA systems. Some units may even be able to power an external speaker cabinet for more volume.