Note: This term is specific to CockroachDB, a Distributed SQL database. In other contexts, it may be used differently.
The Load Balancer is a piece of software added to the front of CockroachDB that helps balance the requests coming into the database. All the nodes in CockroachDB can process requests (they’re all symmetrical), so it makes the most sense to spread the work around between nodes so that the requests can be completed more quickly. The load balancer accomplishes that.