In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2, the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.

Cost is basically unit of work or resource used involved memory, I/Oand CPU to execute the query.Card( or Base cardinality) - is the number of rows in a base table captured by running statistics on the table. If u have incorrect statistics u will be having problem here.Bytes - represents number of bytes accessed by the query.