What does one ring then goes to voice mail mean?

When a phone call rings once and then goes to voicemail, it typically means that the recipient's phone is either turned off, out of service, or they are unable to answer the call. The call may have been screened by the recipient's settings, or they might have declined to pick up. In some cases, it could also indicate that the line is busy, resulting in the call being redirected to voicemail almost immediately.