special session(n = noun.communication) - a session that is held in addition to the regular sessions;
is a kind of session

academic session, bull session, closed session, course session, einstein's special theory of relativity, executive session, in session, jam session, naval special warfare, nothing special, practice session, rap session, saturday night special, session, session cookie, skull session, special, special act, special agent, special air service, special assessment, special branch, special case, special contract, special court-martial, special delivery, special drawing rights, special education, special effect, special forces, special interest, special interests, special jury, special k, special olympics, special pleading, special relativity, special relativity theory, special school, special theory of relativity, special treatment, special verdict, special weapons and tactics squad, special weapons and tactics team, u. s. army special forces, united states army special forces