The Index Spool physical operator contains a SEEK:() predicate in the Argument column. The Index Spool operator scans its input rows, placing a copy of each row in a hidden spool file (stored in the tempdb database and existing only for the lifetime of the query), and builds an index on the rows. This allows you to use the seeking capability of indexes to output only those rows that satisfy the SEEK:() predicate.
If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input.