Conditions are all the properties of a problem (except materials) that can be assigned to an entity.
An example would be the boundary forces and displacement constraints in a solid mechanic analysis or initial velocities in a CFD analysis. Information about contact between master-slave nodes can also be considered as conditions.
Caution: Once a mesh has been generated, any changes made to the condition assignments require you to regenerate the mesh in order to transfer these new conditions. If this new generation has not been performed, GiD will warn you when the data for the analysis is being written.