What is a construct in Oracle?
In Oracle (and other RDBMSs), when an SQL statement is run for the first time, it is cached and if somebody else wants to run a similar statement, the plan is taken from the cache - or shared pool. This is called soft parsing and is less costly than going to the trouble of redoing it entirely. 

So, the term "construct" in this context means an in memory structure (like a "C" struct) which (ideally) allows the database to manage user requests better, like a plan for an already executed query. 

Obviously, having a plan (construct) in memory will improve the server's response time - no need to read disks and recheck indexes &amp;c. which take time. This process is an entire science in its own right.

From here, "The shared pool is like a buffer for SQL statements.  Oracle's parsing algorithm ensures that identical SQL statements do not have to be parsed each time they're executed.  The shared pool  is used to store SQL statements, and it includes the following components"...