What is the difference between terminating an Oracle sql statement with semicolon or with a slash on the next line?
There is no difference for a single SQL statement.  The '/' character on its own line tells SQL*Plus to execute the command in the buffer.  You can use the semicolon at the end of most SQL statements as a shorthand for the '/'.  If you want to execute a PL/SQL block or to execute a handful of SQL statements like CREATE TYPE, however, you need to use the '/'

SQL&gt; begin
  2    null;
  3  end;
  4  /

PL/SQL procedure successfully completed.

SQL&gt; create type foo as object (
  2    col1 number,
  3    col2 number );
  4  /

Type created.


Different tools may have slightly different conventions for how you execute multiple SQL and PL/SQL statements in a script so be aware that this is SQL*Plus specific.