apropos variables (Mastering Emacs

apropos-do-all: if non-nil, most apropos commands behave as if they had been given the prefix argument.
apropos-sort-by-scores: if non-nil, apropos command try to guess the relevance of each result, and display the most relevant ones first.
‘M-x apropos-user-option’: search for user-customizable variables; with a prefix argument, search for non-customizable variables too.
‘M-x apropos-variable’: search for (all) variables; with a prefix argument, search for customizable variables also. This ignores the apropos-do-all variable.
‘M-x apropos-local-variable’: search for buffer-local variables
‘M-x apropos-local-value’: search for buffer-local variables whose values match the specified pattern