What is the difference between centum and satem Indo-European languages?

The distinction between centum and satem languages refers to how different branches of the Indo-European family treated the original Proto-Indo-European palatal stops.12

• Centum languages: In this group, the original palatal stops were preserved as k-like sounds. The term is derived from the Latin word centum ("hundred"), which retains the velar stop. This group traditionally includes Celtic, Germanic, Italic, and Greek.213
• Satem languages: In this group, the original palatal stops underwent a prehistoric sound change, becoming palatal or alveolar fricatives (spirants) or affricates. The term comes from the Avestan word satəm ("hundred"), which illustrates this shift to a sibilant. This group includes Indo-Iranian, Balto-Slavic, Armenian, and Albanian.421

While earlier scholars viewed this as a fundamental split between western and eastern Indo-European groups, modern linguistics places less emphasis on this binary classification. It is now generally understood that the shift to sibilants occurred as a specific sound law within a cohesive dialect area of the parent language.12