Latency (also known as delay) refers to the time it takes a voice packet to reach its destination and is measured in milliseconds. Latency of 150ms or less (one-way) is generally acceptable. Latency greater than 150ms (again, one way) adversely affects the call quality experience.
Your network bandwidth and setup greatly affects whether or not you experience latency or reduced QoS (quality of service).
It's important to check your Network Settings and speak with your ISP if you're having considerable latency issues - RingCentral is simply an end point and has no control over the traffic that is on a network.