(1) To speak. For example, a "push-to-talk" button closes a circuit that allows someone to speak into a microphone.
(2) To communicate. When hardware and software "talk to each other" they are sending messages back and forth according to a protocol. It defines which side starts first, what messages in what format are transmitted or transferred, and which processes take place as a result of those messages.
The industry uses the terms "talk" and "conversation" when describing protocol interactions; however, protocols are rigidly defined unlike human conversations, which are unlimited in scope. One bit or byte out of place in a protocol format and the "conversation" may cease or never start in the first place. See
protocol.