eavesdropping

Short definition from Wiktionary

Noun

1. 1
   verbal noun of eavesdrop: Listening secretly to the private conversations of others.
2. 2
   verbal noun of eavesdrop: The interception of electronic communication.
3. 3
   verbal noun of eavesdrop: The act of one organism listening for another's calls, so as to exploit them.

Verb

1. 1
   present participle and gerund of eavesdrop