通信障害 and 電波障害 literally mean an interference to telecommunication, now used to describe a communication error, or, in today’s (July 2) case, an outage of mobile service. au回線 refers to the network service brand au marketed by KDDI.

Today it has been reported that au network users in multiple areas in Japan experience network outage, with no access to Internet, not even able to make or receive a phone. These users then go tweeting about it on Twitter (using other providers’ network probably), causing the tags to trend.