What is the code variable for ‘censuses’ and how it is define ?
I am afraid I do not understand what you are asking. Please feel free to clarify if I am not addressing your question.
There is no variable ‘censuses’ in IPUMS-International. The variable SAMPLE uniquely identifies every sample within the IPUMS-International database, if this is what you are looking for. The 4-digit code gives the country from which the data was drawn (represented by the 3-digit ISO/UN codes used in the variable CNTRY) followed by a single digit identifying the census year.
I would also recommend looking at the FAQ page, which gives an excellent introduction to the data extract system as well as many links to informative resources. You can also find descriptions of all of the samples here
I hope this helps.