A local instability which can develop in the tokamak when the plasma pressure exceeds a critical value; it therefore constrains the maximum beta that can be achieved. It is analogous to the unstable bulge which develops on an over-inflated pneumatic inner tube.
Resistive Ballooning mode:
A class of ballooning mode which would be stable in the absence of resistivity, but can be unstable in its presence. Related to, but topologically different from, tearing modes.