The S-type (or S-class) is a type of star. When the USS Enterprise arrived in the vicinity of Sigma-285 Trianguli in the 2270s, unnamed stars of this type were noted by sensors. A sputtering S-type, borderline carbon star, had water vapor in its atmosphere, to which Uhura joked to Spock meant the star was "running out of steam". (TOS novel: My Enemy, My Ally)