Unintentional sins or unknown sins.
This is a little known fact, but is true.
I think basically it's never brought up in conversation.
Maybe you could post a link?
Actually offerings for sin, known sin, is also described:
The LORD spoke to Moses, saying,
2“If anyone sins and commits a breach of faith against the LORD by deceiving his neighbor in a matter of deposit or security, or through robbery, or if he has oppressed his neighbor
3or has found something lost and lied about it, swearing falsely—in any of all the things that people do and sin thereby—
4if he has sinned and has realized his guilt and will restore what he took by robbery or what he got by oppression or the deposit that was committed to him or the lost thing that he found
5or anything about which he has sworn falsely, he shall restore it in full and shall add a fifth to it, and give it to him to whom it belongs on the day he realizes his guilt.
6And he shall bring to the priest as his compensation to the LORD a ram without blemish out of the flock, or its equivalent, for a guilt offering.
7And the priest shall make atonement for him before the LORD, and he shall be forgiven for any of the things that one may do and thereby become guilty.”
So it’s not true that offerings are ONLY for known sin.
It’s really a silly position that if you sun and know it, no offering is required. God will just forgive without any cost to you. Only if you unaware of sin do you need a sacrifice on your part. But anyone can see why this is appealing. Choose to Do a nasty deed to someone and you’re forgiven quickly and painlessly.