appositive = relating to or being in apposition,
a word or phrase that is in apposition
apposition (in grammar) = a construction in which a noun or noun phrase is placed with another as an explanatory equivalent, both having the same syntactic relation to the other element in the sentence. One element serves to define or modify the other.
For example Copley and the painter in "The painter Copley was born in Boston."
Only for your better understanding:
It's likely that activists would be in "opposition" of (they will protest against...) having a jail built in a "apposition" (placed together) to a school.
There is another example:
"my friend Alice" the name "Alice " is in apposition to "my friend". Alice, specified to which friend the speaker is referring and is therefore restrictive. On the other hand, in the example "my wife, a nurse by training" the parenthetical "a nurse by training" does not narrow down the subject, but rather provides additional information about the first element, namely "my wife". While a "non-restrictive appositive is almost surrounded by commas, a restrictive-apposition does not require commas in either side.