Looking on the internet deeply has found these results:

plug-in is the most popular phrase on the web.

plug in 13,070,000 results on the web	plug-in 1123,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Or we could plug in a coltrane cd and start our own party right here. Just need to plug in the activation codes, and... there he is. All we got to do now is plug in the numbers. Juno, do you want to plug in the Bunsen burner? This is about domestic violence in particular, but you can plug in other analogues. They should keep her alive long enough to get to Lucy, to plug in the manual override code. Should I plug in, or...? There's nowhere to plug in the phone.	The Cubism plug in. in for loading JPEG2000 images. Added plug in, called Plasma2, with many more options and parameters, is available from the GIMP Plugin Registry. An enhanced version of the Plasma plug in modifies the image so that it appears to be constructed of small squares of semitransparent tissue paper. Added RGB565 support to the csource plug

plug in

13,070,000 results on the web

plug-in

1123,000,000 results on the web

More popular!

Or we could plug in a coltrane cd and start our own party right here.
Just need to plug in the activation codes, and... there he is.
All we got to do now is plug in the numbers.
Juno, do you want to plug in the Bunsen burner?
This is about domestic violence in particular, but you can plug in other analogues.
They should keep her alive long enough to get to Lucy, to plug in the manual override code.
Should I plug in, or...?
There's nowhere to plug in the phone.

The Cubism plug
in.
in for loading JPEG2000 images.
Added plug
in, called Plasma2, with many more options and parameters, is available from the GIMP Plugin Registry.
An enhanced version of the Plasma plug
in modifies the image so that it appears to be constructed of small squares of semitransparent tissue paper.
Added RGB565 support to the csource plug