I mean, scale is also a valid range to include, but I was more thinking about utility and stability. Like, I personally think that a single Raspberry Pi in the corner can be a home lab so long as you're learning something from it. But the thing you're learning on it can be "how do I write a toy HTTP server and the only traffic it gets is me testing it", or "this DNS server is in the critical path for every device on my network". High stakes, low stakes, big, small, careful, YOLO; if you experiment and learn things, it's a (home) lab.