Nano ID uses a 64-character URL-safe alphabet (A-Z, a-z, 0-9, -, _) instead of UUID's hex. With 21 characters you get the same collision resistance as UUID v4, but the ID is 40% shorter.
Use it when IDs end up in URLs or QR codes, `/p/V1StGXR8_Z5jdHi6B-myT` is easier to type than `/p/a8098c1a-f86e-...`.
There's no timestamp or version field, so don't use it when you need sortable IDs.