string.c.doc

Builds a set of characters from the other_str parameter(s) using the
procedure described for String#count. Returns a new string
where runs of the same character that occur in this set are replaced by a
single character. If no arguments are given, all runs of identical
characters are replaced by a single character.

   "yellow moon".squeeze                  #=> "yelow mon"
   "  now   is  the".squeeze(" ")         #=> " now is the"
   "putters shoot balls".squeeze("m-z")   #=> "puters shot balls"