Definition
Unavailable, having taken time off for recreation.
How People Actually Use It
1. To checkout from reality. To be unaware of what's going on. 2. To drop the duties of daily life and go do something else, something nice.
""Honey, you good to go? We agreed today we'd settle the dentist bill, buy new shoes for the kids, drink tea with my mom and then you'd clean the bathroom filter, remember? honey...? Are you there...?" Johnny was gone fishing."
Source: Urban Dictionary