What "Centum" and "Satem" really means is the treatment of the 'palatovelar' series:
In the Centum languages, these become merged with the plain velars (that is, they are treated exactly the same), while in the Satem languages, the palatovelars become fricatives, like
*s and
*z. But this is not universal, for instance compare Latvian "simts", "suns" with Lithuanian "šimtas", "šuo" - meaning "hundred" and "dog", respectively (I might say "hound" instead, because this is the cognate of the Latvian/Lithuanian words, and also actually Centum/Satem-sensitive because the sound in question here is a common
*ḱ....
"canis" > "qen"
"centum" > "qind"
...