Explanation/Answer:
A valve is a part of a shell (a molluscs shell) that can articulate (move). Bivalves are are molluscs that have 2 of these articulated shells, called valves, are named bivalves:
Bi - 2
valves - articulated parts of a shell
Example:
Clams and mussels are both bivalves.
→ Hopefully the image below helps you get a deeper understanding of what bivalves are and look like. Image source: Pinterest.
Hope it helped,
BioTeacher101