A transition model is a model that can be combined with a turbulence model to predict the onset of transition in a turbulent boundary layer. Transition models are necessary because turbulence models themselves cannot be relied upon to predicting the onset of transition.
By the above definition, the transition capability in STAR-CCM+ is not strictly a model, since it does not have a predictive capability. Instead, it allows the user to mimic the effect of transition by suppressing the turbulence in a certain pre-defined region. Using this model also makes two field functions available.