What does onus mean in texting?

Could you clarify for me, what exactly is meant by the term "onus" when it's used in the context of text messaging? I've come across it a few times and I'm not quite sure how it's intended to be interpreted. Is it a slang term that has a specific meaning, or is it simply being used in a more traditional sense that might not be immediately apparent in a text-based conversation? I'd appreciate any insight you can offer on this topic.