siege ramp: a mound of earth and stones heaped up against a city wall so that attackers and battering rams can reach the top
A siege ramp is a long bank of earth and stones piled up against the wall of a city under attack. The Hebrew almost always joins the word to a verb meaning to "pour up" or "heap up," which captures the method exactly: dirt and rubble were dumped and packed down into a sloping road that climbed from the attackers' lines to the top of the defenders' wall. Once the ramp reached wall height, soldiers and heavy battering rams could be pushed up it to break in.
Nearly all of its appearances cluster in Jeremiah and Ezekiel, the two prophets who lived through the Babylonian sieges of Jerusalem. For them and their first hearers this was not a figure of speech but a remembered terror. The word also reaches back to an earlier Israelite siege at Abel Beth-maacah (2 Samuel 20:15) and forward to a Greek-era assault in Daniel 11:15, so the same term stayed in use across centuries of warfare.
In several verses the siege ramp stands beside two other siege terms. The whole operation of surrounding and reducing a city is the siege itself (מָצוֹר); the דָּיֵק is the wall or barrier built all the way around to seal the city off. The ramp is the one piece aimed at a single stretch of wall to force a way in, so the encircling barrier and the assault ramp together name the two halves of an ancient siege: shut the city in, then break it open.
In the prophets the ramp becomes a picture of judgment that cannot be stopped. Sometimes it is God himself who orders the mound poured up against his own city, so that the rising ramp signals that the fall is only a matter of time. In the promise that Assyria would not so much as "pour up a siege ramp" against Jerusalem (2 Kings 19:32), the very absence of the ramp is the sign of rescue.