Slavs are the largest ethno-linguistic group in Europe. Present-day Slavic peoples are classified into East Slavs (chiefly Belarusians, Russians, Rusyns, and Ukrainians), West Slavs (chiefly Czechs, Kashubs, Poles, Silesians, Slovaks and Sorbs), and South Slavs (chiefly Bosniaks, Bulgarians, Croats, Macedonians, Montenegrins, Serbs and Slovenes) .
Slavs can further be divided along the lines of religion. Orthodox Christianity makes up the bulk of the religion encompassing and practiced by the Slavs. The Orthodox Slavs include the Belarusians, Bulgarians, Macedonians, Montenegrins, Russians, Serbs, and Ukrainians and are defined by their use of Orthodox customs and the use of Cyrillic script as well as their cultural influence and connection to the Byzantine Empire (Serbs also use Serbian Latin script on equal terms). The second most practiced and common religion amongst the Slavs is Roman Catholicism. The Catholic Slavs include Croats, Czechs, Kashubians, Poles, Silesians, Slovaks and Slovenes and they are defined by their Latinate influence and heritage and connection to Western Europe. There are also substantial Protestant and Lutheran minorities (especially amongst the West Slavs) such as the historical Bohemian (Czech) Hussites.
The third largest religion amongst the Slavs is Islam. Muslim Slavs include the Bosniaks, Pomaks, Gorani, Torbesis, and other Muslims of the former Yugoslavia as well as certain East Slavs who settled in the Crimean Peninsula and converted to the Islamic faith via influence from the Crimean Tatars.
The oldest mention of the Slavic ethnonym is the 6th century AD Procopius, writing in Byzantine Greek, using various forms such as Sklaboi (Σκλάβοι), Sklabēnoi (Σκλαβηνοί), Sklauenoi (Σκλαυηνοί), Sthlabenoi (Σθλαβηνοί), or Sklabinoi (Σκλαβῖνοι), while his contemporary Jordanes refers to the Sclaveni in Latin. The oldest documents written in Old Church Slavonic, dating from the 9th century, attest the autonym as Slověne (Словѣне). These forms point back to a Slavic autonym which can be reconstructed in Proto-Slavic as *Slověninъ, plural Slověne.
The reconstructed autonym *Slověninъ is usually considered a derivation from slovo ("word"), originally denoting "people who speak (the same language)," i. e. people who understand each other, in contrast to the Slavic word denoting German people, namely němьcь, meaning "silent, mute people" (from Slavic *němъ "mute, mumbling"). The word slovo ("word") and the related slava ("glory, fame") and slukh ("hearing") originate from the Proto-Indo-European root *ḱlew- ("be spoken of, glory"), cognate with Ancient Greek κλέος (kléos "fame"), whence comes the name Pericles, Latin clueo ("be called"), and English loud.