  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.
