a female slave: a woman owned and serving in a household, often one who could be taken as a wife or who calls herself this in humble respect before a superior.
At its core this is one word with one meaning: a woman who belongs to a household as a slave. What changes from place to place is not the meaning but the situation she is in, and the Hebrew Bible uses the word in three recurring situations that are worth keeping in view.
In the law codes she is the household slave-woman, listed beside the male slave and protected from injury and overwork. In several narratives she is the slave a man takes, or is given, as a wife or secondary wife, so the word sits right where slavery and marriage overlap. And in a great many speeches a free woman calls herself by this word when she speaks to a king, a prophet, or God, casting herself as a lowly servant to ask for a hearing.
These are not three different words. They are one status word stretched across a range, from a woman who is literally property, to a woman bound into a household through marriage, to a woman who borrows the language of the slave to show respect she does not owe by law. Scholars have long argued about whether this word and its close partner carry different shades, and the careful recent work concludes they overlap almost entirely, with only a couple of soft tendencies left standing (see the dispute and the related words below).