1. material (for a story, article, etc.); information; news item
from the inversion of たね
新聞部はいつもネタに困ってるからね。The newspaper club is always struggling for material, you know.
2. joke; jest; (comedy) routine; made-up story; material
しかもこのネタ、もう四回ぐらい聞いたヤツだぞ。And I've already heard this joke about four times.
3. proof; evidence
ネタは上がってるぞ？We've got the evidence, you know.
4. (magician's) trick; secret
もうネタは割れてる。We already know how the trick works.
5. ingredients (esp. for sushi)
6. (Internet) meme