"Full-wave" electromagnetic analysis means that the solution is obtained by solving Maxwell's equations for the electric and magnetic fields in the time domain or the frequency domain. This type of rigorous analysis, when performed for the general 3D case, makes no simplifying assumptions about the nature of the EM problem. When using a full-wave 3D EM solver, the usual constraints are solve time and/or problem size.
Other EM analysis methods, such as those based on ray-tracing, usually make an assumption about the problem, such as the object being modeled is large compared to a wavelength. These are used when possible (when all of the assumptions are valid) to avoid the long run-times and size limitations that can accompany general full-wave methods.
Hybrid codes combine a full-wave method with another method (sometimes called high-frequency or asymptotic) to increase the range of problems that can be solved with the tool.