78a - Tipa Ksheira

78a - Rabi Yehuda wants to make a gzeira shava that just as the daughter of a chalal, who was born from "tipa ksheira" (kosher seed) may not marry a kohen, the daughter of a ger, who was not born from tipa ksheira, is certainly not allowed to marry a kohen. (I've discussed this in 2 posts: here & here.)

Sanhedrin 36b says we need 2 psukim to include certain people as eligible to be judges: one to include mamzerim, and one to include geirim, the pasuk is needed because we'd think ger cannot be a judge because he is not from "tipa ksheira," a kosher drop, so the pasuk allows him to be a judge. Ritva, Kiddushin 14a s.v. veha d'amrinan brings this gemara with a different girsa - "tipa serucha," probably translated as putrid drop (see Avos 3:1, Akavia ben Mehallel says look at three things and you will not come to sin...from whence you came - mitipa serucha." There is definitely referring to tipa of a yisrael, but it's trying to tell us from a little, disgusting thing, and is not trying to tell us that the tipa is ad, like the Ritva means.) (Ritva is discussing what I discussed in this post.)

Rambam Isurei Biah 12:13 - to have a child with a shifcha (female slave) is very bad because "the son of a shifcha is a slave and is not Yisrael, and you cause the "zera kodesh" to be profaned and to be slaves..."

Ramban, Igeres Hakodesh Chapter 2 discusses how holy the connection between a husband and wife is - if it's leshaim shamayim. At the end of that chapter he writes "if a man does not intend lesheim shamayim, that zera that comes from him is tipa serucha, and Hashem Yisbarach has no portion in it (as opposed to when it is lesheim shamyaim, there are three partners in the child - the father, te mother and Hashem, as Ramban discussed earlier in that perek), and he is called one who "destroyed his way on the earth;" his body will be destroyed and he will plant an asheira (tree served as idolatry) and will fatten calves for idolatry due to the fact that he emitted zera mekulkal (debased seed)."

So we see how some rishonim use the term tipa ksheira or zera kodesh or tipa mekulakl, etc.