瞎 means blind — so 瞎话 is literally 'blind talk,' words spoken without seeing the truth. Compare: 瞎说 (xiāshuō, to talk nonsense) and 睁眼说瞎话 (zhēngyǎn shuō xiāhuà, to lie with eyes wide open).
register
Colloquial and informal. Used in casual speech to call someone out for lying or exaggerating.
