They probably mean de-fragmenting the tablespace. Tablespace defragmentation only happens when objects are created and dropped and not because of row-level activity. So, it is something the dba wants to keep an eye on. Run this query to check on tablespace fragmentation:

select tablespace_name, block_id, bytes, blocks, segment_name
from dba_free_space
union all
select tablespace_name, block_id, bytes, blocks, segment_name
from dba_extents;

Run the following to de-fragment the tablespaces that are fragmented:

alter tablespace coalesce;

Good luck.