Cross-slot losses –
The magnetic flux prefers to flow through the stator iron material. However, as the stator teeth have higher flux at higher loading, they begin to saturate and the flux will cross through the slots and cut the copper. This will cause additional eddy current losses in the stator copper.
Dielectric losses –
Like hysteresis in magnetic materials, dielectric materials (the insulators) resist the presence of the electric field across them. As the electric field in applied (each cycle of AC voltage) the charge is distributed across the insulators (acting as capacitors) and no capacitor is ideal. They leak charge and they take some small amount of energy to become charged. This amount of energy varies significantly from material to material, and the feature is referred to as the “dissipation factor”. This loss mechanism varies proportionally to frequency and the square of voltage. In high voltage machines (utility generators and transformers) it should not be ignored, and in high-frequency machines, it may not be trivial and sometimes overlooked.
Stray losses –
This sounds like a technical term, but it is really a collection of losses that are from unknown sources that are characterized empirically.