missed call

Short definition from Wiktionary

Noun

1. 1
   A telephone call which the responder does not answer.
2. 2
   A telephone call that is deliberately terminated by the caller before being answered by its intended recipient in order to communicate a pre-agreed message.

Verb

1. 1
   To deliberately terminate a call before the recipient answers in order to communicate a pre-agreed message.
2. 2
   Alternative form of missed call.