What does the Postgres  operator do?
It's supposed to be the "distance" operator from the additional module pg_trgm.

The manual:


  text &lt;-&gt; text   real  Returns the "distance" between the arguments, that is one minus the similarity() value.


The module has to be installed (once per database) with:

CREATE EXTENSION pg_trgm;


More details:


How is LIKE implemented?


Theoretically, any user with the necessary privileges could create an operator with that operator name using CREATE OPERATOR - but not in the example you link to.