I am stuck at understanding the difference between different types of fixed effect models. In particular, what is the difference between:

- A two way fixed effect model in the form of Yit = αi + γt + βXit, where ai is the time fixed effect and yt the entity fixed effect. In the literature this is called two-way fixed effect most of the time
- A fixed effect model in the type of Yit = αγit + βXit where the time fixed effects and the entity fixed effects are combined in "one" estimator. That would mean you would have a time-entity dummy for each combination. Are there any paper regarding this kind of fixed effect model? Is this even a fixed effect approach?

Thank you!