Meaning of CLOSED in English
1》 not open or allowing access.
↘not open to all: the UN Security Council met in ~ session.
2》 not communicating with or influenced by others: a ~ society.
3》 Mathematics (of a set) having the property that the result of a specified operation on any element of the set is itself a member of the set.
4》 Geometry (of a curve or figure) formed from a single unbroken line.
5》 Phonetics (of a syllable) ending in a consonant.
behind ~ doors taking place secretly.
a ~ book a subject or person about which one knows nothing.
Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004