Two quarters or more consecutively in a year the Gross Domestic National Product (US) and in Asia Gross Domestic Product (GDP) show a decline or negative growth value. I am going to use the term GDP = Total Sum of (Goods+Services+Products).
For example, the country shows a decline in GDP (Jan 2019 to April 2019) quarter is 0.5% and then (May to Sept 2019) quarter is 0.0%. Therefore the country is in recession.
There is also another way to define recession which is a recession occurs after a high point in the
level of economic activity and results in a drop in the GNP (or GDP) over two or more quarters, which is then followed by a recovery and a return to a normal state of economic expansion.