Taavah (תַּאֲוָה) means desire or longing — from innocent appetite to consuming lust. The root is avah (H183, to desire, wish for). The word appears in the positive sense (righteous desire), the neutral (appetite), and the negative (sinful craving). The wilderness of Numbers is actually called "Kibroth-hattaavah" — graves of craving.
Desire itself is morally neutral in Scripture — it is what is desired and how that reveals character. Psalm 37:4 promises, "Take delight in the LORD, and he will give you the desires [taavah] of your heart" — sanctified desire, aligned with God. But Numbers 11 records Israel's fatal craving for meat: they received it, and "while the meat was still between their teeth" God struck them. The place became "graves of craving" (Kibroth-hattaavah). The same word that names holy longing names destructive lust. James 1:14-15 maps the path: desire → sin → death.
The root avah (H183) appears 26 times; its most famous nominal form is taavah. Proverbs 13:12 makes the profound observation that fulfilled longing is "a tree of life" — the same tree that appeared in Eden. Desire, properly ordered and fulfilled, is Eden restored. This is Augustine's insight: our heart is restless until it rests in God — because the soul was made with a taavah for God Himself.