  The D-term is a fundamental particle property which is defined through the
matrix elements of the energy-momentum tensor and as such in principle on equal
footing with mass and spin. Yet the experimental information on the D-term of
any hadron is very scarce. The D-term of the nucleon can be inferred from
studies of hard-exclusive reactions, and its measurement will give valuable
insights on the dynamics, structure, and the internal forces inside the
nucleon. We review the latest developments and the fascinating applications of
the D-term and other energy-momentum tensor (EMT) form factors. We also suggest
a definition of the mechanical mean square radius and make a prediction for its
size.
