Network Latency Glossary: Ping, Jitter, RTT, p95 & More
A quick reference of the terms used across the GlobeLatency Learning Center and in latency tools: from anycast and bandwidth to TTFB and TLS. Each entry gives a short definition and links to the guide that explains it in depth.
This glossary explains the vocabulary of latency measurement and networking in plain English. Use it as a quick lookup; each term links to a full guide where one exists. For a structured path, start with What is latency?.
A
Anycast. A routing method where the same IP address is announced from many locations; traffic goes to the nearest one. Used by CDNs and DNS providers. See CDNs and anycast.
API. Application programming interface: how software asks another system for data. API speed depends on network latency plus server processing. See latency for websites and APIs.
Average (mean). The sum of values divided by their count. Sensitive to outliers. See mean, median, min and max.
Asymmetric routing. When packets take different paths in each direction, so outbound and return delays differ.
B
Bandwidth. The maximum amount of data a link can carry per second, in bits per second. Not the same as speed of response. See latency vs bandwidth vs throughput.
Best pass. In GlobeLatency, the lowest reading of a destination in a test; the closest estimate of the path floor.
BGP. Border Gateway Protocol, the system networks use to announce which IP ranges they can reach and so decide internet routes. See routing, BGP and peering.
Bufferbloat. Excess latency caused by oversized queues in network equipment when a link is saturated. See bufferbloat explained.
C
Cache-busting. Adding a unique value to a URL so that caches cannot answer it, forcing a real request. GlobeLatency does this on every request.
CDN. Content delivery network: a distributed set of servers that serve content from a location near the user. See CDNs and anycast and testing CDN performance.
CGNAT. Carrier-grade NAT: many customers share one public IPv4 address at the ISP level. See IP addresses and NAT.
Congestion. Too much traffic for a link or device, causing queueing delay and loss.
CORS / no-cors. Browser rules about cross-site requests. GlobeLatency uses no-cors mode, which allows timing a request but hides the response. See how GlobeLatency measures.
D
Data center. A facility housing servers and network equipment. See data centers, cloud regions and edge.
DNS. Domain Name System: translates names like example.com into IP addresses. See DNS explained.
Down. In GlobeLatency, a destination that gave no successful reply (flag "Down" in a test; red/no reply in live modes).
E
Edge. Servers located close to users at the "edge" of the network, used by CDNs and cloud providers.
Ethernet. Wired local network standard; the lowest-latency way to connect a device at home. See connection types.
F
Fetch API. A browser function for making HTTP requests; GlobeLatency uses it for timing.
Firewall. A system that filters network traffic; can block or delay requests.
H
Hop. One router on the path between two points. More hops often means more delay, though not always.
HTTP/2, HTTP/3. Newer versions of the web protocol that reduce latency effects by multiplexing and (HTTP/3) running over QUIC. See HTTP/1.1, HTTP/2, HTTP/3 and QUIC.
HTTPS. HTTP over TLS encryption. See TLS and the HTTPS handshake.
I
ICMP. Internet Control Message Protocol, used by ping and traceroute. Browsers cannot send it. See ping vs HTTPS latency.
IPv4 / IPv6. The two versions of the Internet Protocol addressing system. See IP addresses, IPv4, IPv6 and NAT.
ISP. Internet service provider. See talking to your ISP.
J
Jitter. Variation in latency from one packet or request to the next. See jitter explained.
L
Lag. A user's perception of delay or stutter; can be caused by latency, jitter, loss or low frame rate.
Latency. The time for data to travel from one point to another. See what is latency.
M
Median (p50). The middle value of sorted measurements. See percentiles explained.
mtr. A diagnostic tool combining ping and traceroute to show loss and latency per hop.
Mixed content. An insecure http resource requested from a secure https page; browsers block it.
N
NAT. Network address translation, letting many devices share one public IP.
P
p95, p99. Percentiles: values that 95% or 99% of measurements stay at or below. See percentiles.
Packet. A small unit of data sent across a network.
Packet loss. Packets that never arrive. See packet loss explained.
Pass. In GlobeLatency, one timed request to one destination; a test repeats several passes per destination.
Peering. Agreement between networks to exchange traffic directly. See routing, BGP and peering.
Ping. A tool (and everyday word) for round-trip latency using ICMP echo.
Propagation delay. Time for a signal to travel a distance; light in fibre goes about 200,000 km/s. See undersea cables and the speed of light.
Q
QUIC. A modern transport protocol over UDP that combines the transport and TLS handshakes and powers HTTP/3. See HTTP/3 and QUIC.
Queueing delay. Time packets wait in line at a router or modem; the main source of latency variation.
R
Region (cloud). A geographic area where a cloud provider runs data centers. See data centers, cloud regions and edge.
Round-trip time (RTT). Time for a request to go out and the reply to return.
Router. A device that forwards packets between networks.
S
Server. A computer that answers requests from clients.
SLO / SLA. Service level objective or agreement: a promised level of performance, often using percentiles.
T
TCP. Transmission Control Protocol: reliable, ordered delivery with retransmissions. See TCP and UDP explained.
Throughput. The actual data rate achieved, which is often lower than bandwidth. See latency vs bandwidth vs throughput.
TLS. Transport Layer Security: encrypts connections. See TLS and the HTTPS handshake.
Traceroute. A tool that lists the routers along a path and the delay to each.
TTFB. Time to first byte: time from a request until the first byte of the response arrives. See TTFB and web performance.
U
UDP. User Datagram Protocol: fast, connectionless, no retransmission; used by games, calls and QUIC.
Unstable (flag). In GlobeLatency, a destination whose worst pass is more than three times its average.
V
VPN. Virtual private network: tunnels your traffic through another server. See VPNs and latency.
W
Wi-Fi. Wireless local network technology; convenient but a common source of jitter. See connection types.
World average. In GlobeLatency, the typical latency visitors get to a destination, used to colour and judge your result. See The world comparison explained.
What to do next
Continue with the FAQ, or run a test and then read Reading your results.
Frequently asked questions
What does RTT mean?
RTT means round-trip time: the time for a message to travel to a destination and for the reply to come back, measured in milliseconds. It is what ping and most latency tools report.
What does ping mean?
Ping is a tool that sends a small ICMP echo request and measures the time until the reply returns. In everyday speech, "ping" has become a word for latency.
What is the difference between latency and ping?
Latency is the general concept of delay; ping is one tool for measuring round-trip latency using ICMP. Other methods, such as timing HTTPS requests, also measure latency.