What does dot forward slash forward slash mean (.//)

It doesn't mean much: the pattern that you gave find was ./, and it is simple for find to glue its results onto that path. A double-slash is ignored (treated as a single slash) except that a leading double-slash could have some meaning for some systems. More important, portable programs assume this behavior.

However, you will see this particular behavior only for BSD-derived systems with an old version of find (OSX for example). NetBSD attempted to fix this in their source in 2005; the userland for OSX is older.

Checking "recent" FreeBSD, NetBSD and OpenBSD, none produce this behavior. Linux and Unix (AIX, HPUX, Solaris) likewise do not.

Further reading:

• Mac Terminal “find” command : What does a double slash in the result output mean?

• pgsql: Remove trailing slashes from directories in find command

• find - find files (POSIX)
  

  The find utility shall recursively descend the directory hierarchy from each file specified by path, evaluating a Boolean expression composed of the primaries described in the OPERANDS section for each file encountered. Each path operand shall be evaluated unaltered as it was provided, including all trailing <slash> characters; all pathnames for other files encountered in the hierarchy shall consist of the concatenation of the current path operand, a <slash> if the current path operand did not end in one, and the filename relative to the path operand. The relative portion shall contain no dot or dot-dot components, no trailing <slash> characters, and only single characters between pathname components.

• How does Linux handle multiple consecutive path separators (/home////username///file)?

• On what systems is //foo/bar different from /foo/bar?