- To come up with a "pop" sound.
The toast is in the toaster - when it pops up it will be ready.
- (idiomatic) To appear without warning.
2013 June 21, Chico Harlan, “Japan pockets the subsidy …”, in The Guardian Weekly, volume 189, number 2, page 30:
- Across Japan, technology companies and private investors are racing to install devices that until recently they had little interest in: solar panels. Massive solar parks are popping up as part of a rapid build-up that one developer likened to an "explosion."
I can't remember where I left my keys, but they normally pop up somewhere.