Specialized schools are secondary schools with enhanced coverage of certain subjects that constitute the specialization of the school. They should not be identified with vocational schools, whose goal is to deliver skills for a particular type of job.
Of the specialized school in the Soviet Union (Russian: Школа с уклоном, Shkola s uklonom) there were three typical types: physical/mathematical schools, with enhanced education in physics and mathematics, sports school, and schools with advanced study of a foreign language of choice. This tradition continued in a number of post-Soviet states, notably Russia, Kyrgyzstan and Belarus, with many schools renamed into liceums.
There also were schools with musical education, but they were in their own category and called "secondary musical school". In secondary musical schools, the primary goal was musical education since the 1st grade (i.e., they may be classified as vocational schools), with obligatory general secondary education provided in a somewhat truncated form. (Note: In the terminology of the Soviet Union, the "secondary school" included primary education as well, i.e., it encompassed grades 1-10.)
Foreign language schools started study of a particular foreign language since the 1st grade (in regular Soviet schools foreign language was introduced in the 5th grade) and, since some grade (commonly the 5th) some subjects were delivered in this language. Language schools specialized in English, German, French, and Spanish languages, with English schools being most common in late Soviet Union and Spanish least common.
Physmath schools (physical/mathematical schools) delivered enhanced education in physics and mathematics. Most commonly, this enhancement started at higher grades, typically starting at 8th or 9th grades.