Cram schools are private businesses that prepare junior high school and high school children for exams. They are very common in Japan, South Korea and Taiwan. The teachers are local people who often may not speak any English outside of the grammar rules and the vocabulary that the students must learn to pass their English tests.
Cram schools are usually contrasted with "conversation schools" were school-aged children and adults go to learn how to speak in English (or attain communicative competence, as linguists would say).
To confuse matters though, in Taiwan and China, the Chinese word for cram school (buxiban) is also used to describe conversation schools.