1-ta‘rif. (1. integral yig’indi yuzchalarning diametrlarining eng kattasi 0 ga intilganda sohani yuzchalarga bo’linish usuli hamda bu yuzchalarda nuqtalarning tanlanishiga bog’liq bo’lmagan aniq limitga ega bo’lsa, bu limit funksiyadan soha bo`yicha olingan ikki o’lchovli integral deyiladi va ko’rinishda belgilanadi