Below mentioned is the description from DESeq2 Vignette for p-values in case for p-adj :

 By default, independent filtering is performed to select a set of
 genes for multiple test correction which will optimize the number
 of adjusted p-values less than a given critical value ‘alpha’ (by
 default 0.1). The adjusted p-values for the genes which do not
 pass the filter threshold are set to ‘NA’. By default, the mean of
 normalized counts is used to perform this filtering, though other
 statistics can be provided. Several arguments from the
 ‘filtered_p’ function of genefilter are provided here to control
 or turn off the independent filtering behavior.

 By default, ‘results’ assigns a p-value of ‘NA’ to genes
 containing count outliers, as identified using Cook's distance.
 See the ‘cooksCutoff’ argument for control of this behavior.
 Cook's distances for each sample are accessible as a matrix
 "cooks" stored in the ‘assays()’ list. This measure is useful for
 identifying rows where the observed counts might not fit to a
 Negative Binomial distribution.