Intra-BSS traffic is traffic between wireless stations in the BSS. When Intra BSS traffic blocking is disabled, wireless station A and B can access the wired network and communicate with each other. When IntraBSS traffic blocking is enabled, wireless station A and B can still access the wired network but cannot communicate with each other.
The best practice for intra-BSS traffic Blocking is to only enable it for Guest WiFis, which are for clients that you don't trust.
How to enable or disable Intra-BSS Traffic Blocking
Configuration -> Object -> AP Profile -> SSID -> SSID Profile