Physics uses fields to describe physical quantities that have a value for each point in space. For example; the temperature in a room is given by a field, the breeze in a room is given by a field. These two fields are not of the same kind, though. The temperature assigns a single value to each point. For example, over the radiator the temperature field says 30 C (86 F in freedom units) and next to an open window 8 C. While the breeze field assigns a vector (a little arrow) to every point in space. Over the radiator, a small arrow pointing up indicating air is flowing with a small speed upwards as the hot air raises. Next to the window a bigger arrow pointing inwards into the room, indicating the breeze is stronger and entering the room.

Different kinds of fields do not transform the same as you change your point of view in the room. If you rotate your point of view, the temperature field remains invariant. For the same point in space you assign the same temperature. But the breeze field changes as you change your point of view with a rotation. If you look directly to the window the breeze in the window points against you, if you face in the opposite direction it points in the same direction you are looking. A rotation changes the breeze vector but leaves the temperature vector unchanged.

How these different fields change as you rotate your point of view is what spin describes. It's a property of the field. The temperature field has spin 0, the breeze field has spin 1.

Fundamental particles are defined by fields too. The electron is defined by a field, the photon is a field, the Higgs boson is a field, the graviton is a field... As fields they have this property characterizing their behavior under rotations.

The Higgs boson is given by a spin 0 field (like the temperature example above). Rotations leave the field invariant.

The photon is given by a spin 1 field (like the temperature example). Rotations make the field changes such that a complete 360 rotation leaves the field invariant.

The graviton is given by a spin 2 field. Rotations make the field change such that a half rotation leaves the field invariant.

The electron is given by a spin 1/2 field. Rotations make the field changes such that you need to do 2 full rotations to leave the field invariant.

Spin characterizes their behavior under rotations. As physics is invariant under rotations this property is a conserved quantity.

Of all of this, the only mind-bending stuff is that a spin 1/2 field requires 2 rotations to leave it invariant. So here is a visualization: https://upload.wikimedia.org/wikipedia/commons/a/a9/Belt_Tri...