The activities which contribute to the Gross National Product (GNP) of a country are called 'economic activities'. They are the productive activities of the economy, which are always undertaken for earning some monetary reward in return.
For examples: a teacher teaching in a class, a doctor attending to his patients in a clinic, rickshaw-puller carrying a traveller etc.
All the above, i.e., teacher, doctor and the rickshaw-puller are indulging in economic activities of various kinds.