High-confinement mode; a state of magnetically confined plasma where a significant density and temperature gradient forms at the edge of the plasma and the confinement time is prolonged. The H-mode was first observed on the ASDEX tokamak in 1982 in plasma heating experiments using NBI. Since then, it has been achieved on all magnetic confinement devices worldwide. In H-mode, a transport barrier, i.e., a reduction of turbulence at the edge of the plasma occurs, which improves the confinement of particles in the core of the plasma and sets the conditions for fusion to take place. However, the H-mode brings with it a potentially dangerous instability called Edge Localised Modes. The previous mode with insufficient confinement time was named L-mode, Low-confinement mode.