Final answer:
A conglomerate is a geological term for a rock with rounded clasts in a finer-grained matrix; it is a clastic sedimentary rock distinct from sandstone and shale.
Step-by-step explanation:
The geological term used to describe a rock composed of rounded clasts in a finer-grained matrix is conglomerate. Conglomerates are a type of clastic sedimentary rock that is characterized by the presence of rounded gravel-sized particles that have been cemented together in a matrix of finer sediment. This contrasts with sandstone, which is composed of sand-sized minerals or rock fragments, and shale, which is a fine-grained clastic rock with fine laminations and is more fissile due to its layer structure.