Ricci Calculus is a set of mathematical tools used by scientists and mathematicians to help understand and interact with space and time. It is named after the Italian mathematician Gregorio Ricci-Curbastro, who developed the ideas in the late 19th century. Ricci Calculus is used to solve problems in physics, particularly those involving curved surfaces, like the Earth and the shape of the Universe. It helps us to figure out how objects can move through curved space and time, following certain laws, such as the famous 'law of gravity'. Ricci Calculus is like a set of mathematical tools in a toolbox that scientists and mathematicians use to study and answer questions about curved things in the universe.