Cross section
From Particle Wiki
The cross section for a given process is a measure for the rate of interactions that orininate from the process that can be quoted independently of the experimental set-up of the scattering experiment itself.
Cross sections are measured in units of area, where the special unit barn (b) is used with prefixes. Cross sections at the LHC can range from hundreds of millibarns (the total cross section of proton-proton collisions) down to fb or smaller for rare processes that are still considered to be measurable.
