A Hebrew word meaning something like "presence" (well, not really; you wouldn't use it for "in my presence" or something like that.) Specifically, the presence of God. It's derived from the root meaning "to dwell." Because the word is grammatically feminine, it is used in Reconstructionist Judaism (and other movements aiming to make the religion less masculinized, in their view) as term for God in a more female light. Or the "female God" if you prefer. Presumably, God is not "male" nor "female," but has aspects of both (or both have aspects of him, or whatever your personal theology demands), but Hebrew only has two genders and God seems always to be referred to in masculine, so this allows a feminine angle.
There's probably some kabbalistic basis to this as well; I am not an expert in this particular aspect of belief.