What is “Oracle Access”?

I'm reading a paper for school and I have come across a passage that I don't understand. It says "If we allow the query to access the entries of the array through an oracle, it is possible to obtain a data structure of sublinear size".

Searching for information on what Oracle Access is has given me nothing but stuff about Oracle Databases, which is obviously not what I'm looking for. I can't really wrap my head around what this means.

Can anyone point me in the right direction?

An oracle is basically a magic black box that does something (e.g. query the entries of an array), usually in constant time. How the oracle does this is abstracted away from (and sometimes an oracle might even do something impossible like solve the halting problem). It's just a way of saying "presume we had these computational abilities, then ...".

StackExchange Computer Science Q#40536, answer score: 12