CM type of a CM field?

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I am reading a paper by Colmez, it is titled - "Fonctions zeta p-adiques en s=0". It is completely in French and I am using Google translate to convert it. There is one line which Google translates in something which I couldn't make sense of.

Here's the line -

(in French) :- "Si K est un corps CM, un type CM de K sera par definition un sous-ensemble de $Hom(K,\overline{Q})$ tel que l'application de $\Sigma$ dans $S_{\infty}$ soit une bijecition"

translates to

(in English) :- "If K is a CM field, a CM type of K will be by definition a subset of $Hom(K, \overline{Q})$ such that the application of $\Sigma$ in $S_{\infty}$ is a bijecition."

where $S_{\infty}$ is the set of all archimedean valuations on K and $\overline{Q}$ is algebraic closure of $Q$ (the rationals).

I don't understand what this application means?