Centum and satem languages

Languages of the Indo-European family are classified as either centum languages or satem languages according to how the dorsal consonants (sounds of "K", "G" and "Y" type) of the reconstructed Proto-Indo-European language (PIE) developed. An example of the different developments is provided by the words for "hundred" found in the early attested Indo-European languages (which is where the two branches get their names).

Source: Wikipedia — Centum and satem languages (CC BY-SA 4.0)