load kpa?

hello. here, LOAD was mentioned on the graphs' X axis. please explain this 'load' ? is it the mass of air on the piston, psi, combustion heat ?? i'm unsure what to make of it exactly.

hello load is measured as kpa map and mgp all are a directive of pressure. in a non boosted application more load is meaning the closer the map reading is to atmopheric pressure the more load is being applied. similar in bosted applications but the load is carried on with direct relation to boost