The R-number (or R-ratio, basic reproductive number, basic reproduction number, basic reproduction ratio or basic reproductive rate) is the number of people that one infected person will pass the virus on to. It can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.
The R-number is not considered to be a biological constant for a given infection. It is affected by other factors such as environmental conditions and the behaviour of the population that has been infected. As such, lock down provisions that reduce the rate of transmission, reduce the R-number.