"Pin" and "skewer" are fairly common terms in chess:
A pin is a situation where a piece cannot move without exposing a more valuable piece to attack. For example, the Ruy Lopez Opening features a black knight pinned (against the black king) by a white bishop after white's third move.
A skewer is when a piece is attacked and moving it would expose a less valuable piece to attack. An example would be a black rook attacking a white queen along a file with a white rook on the same file behind the queen.
However, I am unaware of a term applying to a similar situation in which the attacked piece is of equal value to the piece it is shielding, whether because they are two pieces of the same type (e.g. rooks) or the same value (bishop and knight, using "conventional" values of 3 pawns/points for both knights and bishops). Does such a term exist? If so, what is it? Or do we just use "pin" (or "skewer")?
The diagram shows an example with a white bishop attacking two black rooks along the same diagonal. (The black pawn is to rule out the possible responses Ra5 and Rb5, which distract from the point of the example.)
r7/1r2k3/8/1p1BK3/8/8/8/8 w - - 0 1
3kq3/3p1p1p/8/4R2b/3P4/4K3/8/8 b - - 0 1
, even though white can only take the bishop if the queen moves — I think most people would consider these kinds of positions as fork.