An up fold in rock is:

In geology, an up fold in rock strata is known as an anticline. These structures are undulating, wave-like deformations that form when the Earth's crust is subjected to compressional stress [1]. An anticline is specifically characterized as being upwardly convex, often resembling the shape of the letter 'A' in cross-section [2]. In these folds, the oldest rock layers are located at the core or center, while the younger layers are found on the outer flanks [3]. Conversely, a downward fold is termed a syncline, which forms a trough-like structure with younger rocks at its center [1]. Other terms like graben and horst refer to blocks of crust displaced by faulting rather than folding; a graben is a down-dropped block, while a horst is an upthrown block between faults [4].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 10: Types of Mountains > Fold' In Geology > p. 134
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 10: Types of Mountains > Dip-Slip Faults > p. 138
3. [3] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geological-fault
4. [4] https://en.wikipedia.org/wiki/Horst_and_graben