It is "a complementary English course book for computer science students and their teachers." Basically, for people learning a foreign language, those learning

It is "a complementary English course book for computer science students and their teachers." Basically, for people learning a foreign language, those learning often need to learn a _specific subdomain_ of the language. If you're a computer science student, there's a lot of English you need to know there that you would not find in a general ESL (English as a Second Language) course. This is an English textbook for computer science students. It contains standard learning-English components, such as short essays on topics followed by questions to demonstrate understanding, but all those topics are around computer science.