Seki's Calculus refers to the mathematical work of Seki Takakazu, a Japanese mathematician from the 17th century. He developed a unique approach to calculus, focusing on the study of infinitesimals and the concept of limits, which laid the groundwork for later developments in mathematics. Seki's methods included techniques for solving problems related to areas and volumes, similar to those found in European calculus. His work was largely independent, and he contributed significantly to the understanding of mathematical concepts in Japan, influencing future generations of mathematicians.