General acid/base catalysis is a type of catalysis that involves the use of a molecule, other than water, that can donate or accept a proton. Histidine is a common participant in general acid/base catalysis because its side chain has a pKa around 7, which means it can act as both an acid or a base under physiological conditions. This makes histidine a versatile participant in catalysis, allowing it to donate or accept protons as needed to promote chemical reactions. Overall, general acid/base catalysis and the role of histidine in this process are important concepts in biochemistry and enzyme catalysis.