It is a purpose-built or adapted trailer designed to carry a tiny house structure on the road. Key specs include length, width, axle count, and gross vehicle weight rating (GVWR).
You need a trailer rated for the finished weight and dimensions of your build. Check local road limits for width and height, and confirm the trailer manufacturer allows your intended use.
Used trailers can save money if the frame, axles, and brakes are in good condition. Inspect for rust, bent frames, and worn tires. Verify the title transfers cleanly before you commit.