A depiction of an exhaust port located on the first Death Star.
A thermal exhaust port functioned as a release valve, getting rid of the extra heat generated by the enormous energy reactors utilized within starships, space stations, or certain land-based installations. These ports moved surplus thermal energy away from reactors and other systems within a structure, venting it into the surrounding space or atmosphere. This process was crucial to prevent system failures or harm to personnel resulting from excessive heat accumulation.
Notably, thermal exhaust ports were often susceptible to being damaged or deliberately sabotaged. Detonating something inside an exhaust port could set off a cascading explosive event, leading to the main reactor reaching a critical state and subsequently exploding. Consequently, these ports were frequently defended, either through physical barriers or by employing ray shielding to protect against energy-based weaponry.
The destruction of the initial Death Star by Luke Skywalker serves as a famous example of how critically exposed and neglected the placement of these ports could be. The Death Star's thermal exhaust port was a considerable design flaw that the Rebels successfully took advantage of during the Battle of Yavin. Because of this event, the thermal exhaust ports were removed from the design of the Death Star II, however, the Death Star III still had this vulnerability.
As another illustration, Imperial Robotics Construction Facility Ice Station Beta met its end when Kyle Katarn strategically placed sequencer charges within thermal exhaust ports throughout the facility.