Hi,
This scenario usually applies to Cisco Nexus Series switches, where the exit for hot air from the switch could be in the back or front side.
So, port side intake means the cold air enter the switch where the ports are and port side exhaust means hot is exiting from the port side. With Nexus switch you have the option to intake in front or the back.
For more info refer to this document:
Standard-airflow fan: This option provides front-to-back airflow, with ports aligned with the hot aisle (port-side exhaust). This option is ideal for ToR deployments to align the fabric extender ports with the server ports in a given rack
• Reversed-airflow fan: This option provides back-to-front airflow, with ports aligned with the cold aisle (port-side intake). This option is ideal for network rack deployments in which various network equipment ports need to be aligned
Link:
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-2000-series-fabric-extenders/product_bulletin_c25-680197.html
HTH
