Budapest Rook
The "Budapest rook" is a manoeuvre, introduced by the IM Dolfi Drimer in 1968, with which Black develops the a8 rook aggressively along the sixth rank using the moves a7–a5 and the rook lift Ra8–a6–h6. For example, this can happen in the Adler variation after the move sequence 1.d4 Nf6 2.c4 e5 3.dxe5 Ng4 4.Nf3 Bc5 5.e3 Nc6 6.Be2 Ngxe5 7.Nxe5 Nxe5 8.a3 a5 9.0-0 0-0 10.Nc3 Ra6 11.b3 Rh6.
The rook is then used to support a piece attack against White's castled King. Black can easily get several pieces around the white king, notably a rook to h6, a queen to h4 and a knight on g4. The queen's arrival on the h4-square is facilitated by the absence of a white knight on the f3-square (that would otherwise cover the h4-square) and of a black knight on the f6-square (that would block the way for the black queen). If White tries to defend with h2–h3, this may allow the Bc8 to be sacrificed at h3 in order to open the h-file.
The Bc5 may not seem particularly useful in this attack, but by eyeing e3 it makes it difficult for White to play f4 to chase away the black knight; furthermore, the attack on e3 is sometimes intensified with major pieces doubling on the e-file. Besides, the Bc5 can sometimes be recycled to the b8–h2 diagonal via Bc5–a7–b8, to apply still more pressure on h2. It can also stay on the a7–g1 diagonal to put pressure on f2, if White pushes e3–e4 at some stage.
The "Budapest rook" was an invigorating innovation of the 1980s, and gave the gambit new life. However, inconveniences arise from delaying d7–d6 in order to allow the lift: the light-square bishop has to wait a long time to develop, and any attack on the Bc5 is potentially annoying for Black (since it means either closing the sixth rank with ...d6/...b6, abandoning the active a7–g1 diagonal, or blocking the rook when deployed to a7). This, in addition to the risk of awkwardness in the king side (a knight on f5 will fork the Rh6 and the Qh4) and the single-mindedness of Black's plan (with nothing to fall back on if the direct attack is repelled), has made some revisit the old lines, where it is instead the king's rook that is developed to h6. The queen's rook can then be retained on the queenside, and will be well-placed if the b-file opens as a result of Black's Bc5 being exchanged and recaptured with a b6 pawn.
Read more about this topic: Budapest Gambit, Strategic and Tactical Themes