An invisible term refers to a service or product that cannot be seen or touched physically. Among the options provided, "banking services" is an invisible term because it refers to the various services provided by banks such as loans, deposits, and credit facilities, among others. These services cannot be seen or touched as they are intangible. On the other hand, "petroleum products," "processed rice," and "processed milk" are all visible and tangible products that can be seen and touched physically.