To pass gas; to break wind, to fart.
To vent, usually, to reduce pressure in a container.
The radioactivity was released when they blew off steam from the containment vessel.
To let steam escape through a passage provided for the purpose.
The engine or steamer is blowing off.
To shirk or disregard (a duty or person).
I decided to blow off the meeting and leave early.
To forcibly disconnect something by use of a firearm or explosive device.
Her leg was blown off by a landmine.