There is no official weight definition of “ultralight backpacking”. It’s more a frame of mind than an arbitrary pack weight. It’s about deciding you can get by with less. But for me, I tend to think that a base weight (i.e. not counting consumables such as food, water, or fuel) of 4.5 kg (10 lbs) or less qualifies.
Here is my three-season hiking (or fastpacking) gear review. Read more (in Swedish) in my gear section.
And you can actually trailrun with this setup (i.e. ”fastpacking” – or adventure running):