CLUSTERNO (V001) reports the cluster number for the person's de facto residence.
According to the DHS Sampling Manual, "A cluster is the smallest geographical survey statistical unit for DHS surveys. It consists of a number of adjacent households in a geographical area. For DHS surveys, a cluster corresponds either to an [enumeration area], or a segment of a large [enumeration area]." The most recent census for a country, which divided all territory into enumeration areas to ensure full coverage of the population, often provides the sampling frame for a DHS survey.
CLUSTERNO is the variable indicating the primary sampling unit or PSU. It should be used along with the variable STRATA to account for the impact of the sample design clustering on the estimates of variance and standard errors.
See the notes on DHS webpage "Use sample weights" [URL omitted from DDI.] on variance estimation for additional information.
CLUSTERNO (V001) and HHNUM (V002) can be used to merge the women's individual recode file to the household recode file. See the DHS webpage Merging Datasets [URL omitted from DDI.] on variables to be used for linking data sets.