What is ROFL in chat?

I'm curious, could you please explain what ROFL means in online chat? I've seen it used quite frequently, but I'm not quite sure what the acronym stands for or how it's used in context. I'm interested in understanding the origin of this term and how it's evolved over time in the online community. Is it considered a formal or informal way of expressing laughter or amusement? And are there any other similar acronyms that are commonly used in chat conversations?