Slovak is actually a West Slavic language and is the language spoken in the central European country of Slovakia. It is used by the majority of the Slovakian population, with there estimated to be five million native speakers.
The language is very closely related to Czech and, to a lesser extent, Polish. Both Slovak and Czech distinguish themselves from other Slavic languages because the stress is typically placed on the first syllable of a word.
While most Slovak speakers are residents of Slovakia, it is also spoken in the United States, which is actually home to the highest number of Slovak emigrants, plus the Czech Republic, Poland, and several other countries.