Be off
1 leave 2 not happening
1 Leave

Meaning
Leave a place.
Why Off?
We use the preposition/adverb off to say that something or someone is not there. It's gone.
Examples
| I'm just off to see the solicitor. I should be back around lunchtime. |
| I'll be off then. See you later. |
| We're off to grab a bite to eat. Do you want to join us? |
| I'm off. Wish me luck. |
| We're off to Spain for a well deserved break. |
Grammar
inseparable
Don't separate this phrasal verb in this context.
Someone is off.
| He is off on holiday. |
| I'm off to the shops. |
2 Not happening
Meaning
Leave a place.