Topheth is in the Valley of the Son of Hinnom, where child sacrifice is described, and God says it will be called the Valley of Slaughter (Jeremiah 7:31–32). The passage says many will fall and there will be no place to bury them (Jeremiah 7:32–33).
In Jeremiah 7:29–34 Jerusalem is told to mourn publicly because Yahweh has rejected the present generation. The reason is concrete: Judah placed offensive objects in the temple and built Topheth in the Valley of Hinnom to burn children—something Yahweh insists he never commanded. This unit continues the temple-focused confrontation in Jeremiah 7, where trust in sacred space and rituals is exposed as empty when paired with destructive practices.
This passage presents a public, communal collapse. Jerusalem is pictured as a grieving person (shaved hair, lament on the exposed ridges) because Yahweh has “rejected and forsaken” the current generation. The stated reasons are not vague: Judah brought “abominations” into the temple and practiced child-burning at Topheth in the Valley of Hinnom.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Jeremiah 7:31-32, then read the surrounding section so the answer stays connected to the passage's flow.
31They have built the high places of Topheth, which is in the valley of the son of Hinnom, to burn their sons and their daughters in the fire; which I didn`t command, neither came it into my mind.
32Therefore, behold, the days come, says Yahweh, that it shall no more be called Topheth, nor The valley of the son of Hinnom, but The valley of Slaughter: for they shall bury in Topheth, until there be no place [to bury].