Final answer:
A horst is an uplifted block of Earth's crust found between two downward-moving normal faults. It differs from a graben, which is a lower block between faults, and should not be confused with folds like anticlines and synclines.
Step-by-step explanation:
An uplifted block bounded by two normal faults is known as a horst. When the crust extends, it can lead to the formation of features such as grabens and horsts. In this scenario, a horst is a raised block of the Earth's crust that sits between two normal faults that have moved downwards, which contrasts with a graben which is a lowered block of crust between two normal faults.
Grabens and horsts are significant because they are indicators of tectonic activity and can influence the topography and geological structure of an area. Normal faults occur when the Earth's crust is under extensional forces, causing the hanging wall to move down relative to the footwall. In the case of horsts and grabens, the horst remains elevated while the surrounding grabens subside.
It's important not to confuse horsts and grabens with anticlines and synclines, which are folds, not faults. Anticlines are arch-like folds in the crust where the oldest layers are at the core, and synclines are trough-like folds with the youngest layers more centrally located.