Definitions
There are 2 meanings of the phrase
On Tap.
On Tap - as an adjective satellite
(of liquids) available by turning a tap
Example: "Ale on tap"
Available for immediate use
Example: "Extra personnel on tap"
Example Sentences
"There are several craft beers on tap at this bar."
"Do they have any IPAs on tap?"
"We have a wide selection of local beers on tap."
"They have a rotating selection of beers on tap."
"I prefer to drink beer on tap instead of bottled."