What "Centum" and "Satem" really means is the treatment of the 'palatovelar' series: [TABLE="class: cms_table"]
[TR]
[TD]*ḱ,[/TD]
[TD]*ǵ,[/TD]
[TD]*ǵʰ[/TD]
[/TR]
[/TABLE]
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"
...