In simple words, public debt refers to the loan raised by the government within the country or outside the country. The government may borrow from individuals, business enterprises and banks, etc. when its expenditure exceeds its revenue. But it is not a source of revenue like tax.
Public Debt is the money owed by the Union government, while private debt comprises of all the loans raised by private companies, corporate sector and individuals such as home loans, auto loans, personal loans.