The 4051BDM is an analog multiplexer / switch from the * series, built for routing analog or digital signals in a single-pole 8-throw (SP8T) configuration.
Packaging and compliance — the fine print for your BOM
The RoHS non-compliant status is a hard flag: if your assembly line is RoHS-only (lead-free solder), this part won't pass incoming inspection. That's a sourcing constraint you need to know before you spec it into a new design or a legacy repair.