Czech is classified as a member of the West Slavic sub-branch of the Slavic branch of the Indo-European language family. Slovak is by far the closest genetic neighbour of Czech, and the languages are closer than any other pair of West Slavic languages.
"Spisovná čeština" refers to the formal, written form of the national language, which is used in official documents, in literature, at school and in the media. Its rules are found in dictionaries and grammar handbooks and are overseen by the Czech Academy of Sciences' Institute of the Czech Language. The spoken form of this formal language is known as "hovorová čeština".
"Obecná čeština" is an informal variant of the language, which is simplified and has a slightly different morphology, vocabulary and pronunciation. It is used in everyday conversation but is not considered "correct" in written or formal communication.