The Azure Load Balancer (ALB) is responsible for routing incoming traffic to your role instances. In order for the traffic to be correctly routed, ALB must first send a query to the respective endpoints and check that the URI returns a HTTP 200 OK code. This process is called load balancer probe.
In other words, the load balancer probe is a customer defined health probe of endpoints in your role instances.
A LoadBalancerProbes is not a standalone element, but exists in combination with a WebRole or a WorkerRole. A LoadBalancerProbes may be provided for more than one role.
A template of a LoadBalancerProbes element looks like this:
<ServiceDefinition ...>
<LoadBalancerProbes>
<LoadBalancerProbe name="<load-balancer-probe-name>"
protocol="[http | tcp]"
path="<uri-for-checking-health-status-of-vm>"
port="<port-number>" intervalInSeconds="<interval-in-seconds>...