Form factors are Lorentz invariant functions describing the internal structure of a system. In particular, they encode how physical properties like, e.g., charge, energy, momentum, and pressure are spatially distributed. While nucleon electromagnetic form factors have been studied for a long time, the first extraction of nucleon gravitational form factors from experimental data was reported in 2018, triggering a lot of enthusiasm and attention in the hadronic community. In this contribution we review some theoretical bases, discuss recent developments regarding the physical interpretation of these form factors, and give a glimpse of what can be learned about the mass and spin structure of the nucleon.