Definition of topsoil is unclear to me

Hi, in our construction contract it states that it will be filled with 15 cm of topsoil, do I have to accept it as it is shown in the picture here. According to various sites, it is always the top layer, but then everything on the surface would be "topsoil". Thank you

Topsoil can have different qualities. I don't believe that quality claims can be made unless something more specific was mentioned in the contract.

Get a soil survey first, only then will you know what actually needs to be done. Everything else is assumptions and those can cost €5000-€50000 ;)

The soil seems relatively sandy to me, which doesn't necessarily have to be a bad thing. How deep can you dig with a normal spade, and what is the soil like "inside"? High proportion of large stones? More clay? Or does it also have dark parts that suggest humus? In our case, the topsoil wasn't particularly good either. The proportion of stones and clay was quite high. If you want to get really good garden soil, rent a powerful rototiller, plow the soil once, collect all the stones, and work in a lot of compost. In our area, they have it at the local composting plant for a nominal fee for delivery (I paid €40 for 12 cubic meters). Distribute everything, till it all again with the rototiller, and the garden soil is perfect.

Topsoil is not a technical term. What you probably should have ordered is called substrate or topsoil mixture.

As you already say, it can be anything that is on the surface. But no problem, go over it twice with a rotary tiller, pick out the big stones, add some fertilizer and grass on top, and you won’t see any of it anymore.

The soil looks quite normal at first. Topsoil should be fairly nutrient-rich, which you cannot tell from the picture. The topsoil can be sandier or more loamy. An organic content is not specified. Maybe you expected a layer like directly under a turf layer, then I understand the disappointment. I do not see a reason for complaint in the picture. Much more important for a successful garden is that the entire area has not been compacted.