At its base, it is a system that takes a programmatic score, as well as programmatic descriptions of synthesized instruments or processors, and produces audio o

At its base, it is a system that takes a programmatic score, as well as programmatic descriptions of synthesized instruments or processors, and produces audio output. Other tools in this category include CLM, Supercollider, and STK, though Csound has a history that predates all of them. What makes it different from popular music tools is that you are in control of the instruments' guts, and can create custom instruments, so you can apply virtually any form of synthesis, any type of audio transformation or generation, you can imagine. This makes it ideal for experimenting with synthesis and algorithmic composition. "Electro-acoustic" is an academic term that encompasses various forms of experimental music and research involving artificial sound sources, including electronic music, electric instruments, tape loops and manipulation, computer-generated music, and so forth. Roughly: "any avant-garde music that requires loudspeakers to perform." You can of course use Csound for more popular music applications as well, but you would typically find traditional DAW tools to be more convenient in those cases.