Reference
In plain terms
An alias to an existing value, often a safer form of pointer.
Going deeper
A reference points to another variable's data, letting code access or modify it without copying, typically with more safety than raw pointers. Passing by reference avoids expensive copies.
Under the hood
References can't usually be null or reseated (in C++), reducing pointer pitfalls; managed languages pass objects by reference implicitly.
Examples
C++ references, Java/Python object references, pass-by-reference parameters.
Think of it like...
Like a nickname that always refers to the same person, no separate copy of them exists.