Renormalization: in particle physics the behaviour of particles in the smallest scales is largely unknown. In order to avoid this difficulty, the particles are treated as fields behaving according to an "effective field theory" at low energy scales, and a mathematical tool known as renormalization is used to describe the unknown aspects of this effective theory using only a few parameters.
In particle physics, understanding how particles behave at extremely small scales is difficult. To address this, physicists use an "effective field theory" that describes these particles' behavior at low energies. Renormalization is a mathematical tool used to describe the unknown aspects of this effective theory using only a few parameters.