Latency is the delay experienced along a network path. For a network task, it describes the time taken for traffic or a response to travel along the relevant path. A displayed ping usually concerns a round trip to a particular destination, so the destination and test method matter.
A practical example
Imagine two connections that can download the same file quickly. One may still make a call or an online game feel less responsive because the response arrives later. A large download-speed number is not a substitute for observing delay.
What to check
Compare the same destination from the same device and network. Record a range over a short session rather than one unusually good result. If you change both the Wi-Fi network and the selected server, you cannot tell which change affected the delay. Repeat a normal task to check whether the difference is noticeable.
What it does not tell you
Latency is not a measurement of privacy or encryption strength. A low ping also does not rule out packet loss or unstable timing. Look at the symptom you are trying to solve before concluding that a connection is better.
Read the technical reference for the underlying definition. For a connection that is failing now, use the troubleshooting guide. To choose an app, follow the VPN selection worksheet.