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Glossary · 18 terms

Plain definitions of everything you'll meet.

Vendor docs and FAQs love jargon. Here's a flat list of the terms that come up while buying or installing an eSIM, each with a short definition + practical context.

4G LTE
fourth-generation Long-Term Evolution
The dominant cellular generation since 2012. Typical real-world speeds: 20–80 Mbps download, 5–20 Mbps upload, with 30–50 ms latency.
5G
fifth-generation cellular
The current generation of cellular network technology, offering peak speeds 10-100× faster than 4G under ideal conditions. In practice, urban 5G hits 200–500 Mbps depending on the carrier and spectrum.
carrier lock
phone restricted to one carrier
A software restriction that prevents a phone from using SIMs (physical or eSIM) from carriers other than the one it was originally sold by.
data cap
monthly data limit
The maximum amount of data a plan provides at full speed. Above the cap, behavior varies by provider: slow speeds, extra charges, or disconnect.
dual SIM
two active lines on one phone
A phone configuration where two SIM lines (any combination of physical + eSIM) can be active simultaneously. Common patterns: home physical SIM + travel.to eSIM, work eSIM + personal eSIM, primary + backup.
eSIM
embedded SIM
An eSIM is a digital SIM card embedded directly into your phone's hardware. Unlike a physical SIM, it's a software profile downloaded via QR code, no plastic chip required.
eUICC
embedded Universal Integrated Circuit Card
The hardware chip inside your phone that holds eSIM profiles. The "embedded" version of the traditional UICC found in physical SIM cards.
fair use policy
limit on "unlimited" plans
A clause that caps the speed (or sometimes disconnects) of unlimited plans after a customer crosses a high usage threshold, to prevent infrastructure abuse.
ICCID
Integrated Circuit Card Identifier
A 19-22 digit number that uniquely identifies a SIM (physical or eSIM) globally. Think of it as a serial number for the SIM profile.
IMEI
International Mobile Equipment Identity
A 15-digit number that uniquely identifies a phone. Used by carriers to authenticate the device on their network.
LPA string
Local Profile Assistant activation string
The text-format encoding of an eSIM activation profile, used when a QR code can't be scanned. Looks like: LPA:1$smdp.example.com$matching-id.
eSIM profile
one installed eSIM
A single eSIM identity installed on your phone's eUICC. Each profile has its own ICCID, carrier credentials, and APN settings. Phones can hold multiple profiles, with one or two active simultaneously.
QR code
two-dimensional barcode
A square barcode that encodes a small amount of text — for eSIM activation, it encodes an LPA string. Your phone's camera reads the QR and extracts the activation profile.
refund
getting your money back
Travel.to's refund policy: full refund if the eSIM fails to activate; half refund if it activates but underperforms (or you used less than 500 MB before the issue surfaced).
international roaming
using your home carrier abroad
A service offered by mobile carriers that lets your home phone number work in foreign countries, by routing through partner networks. Typically costs $10–25 per gigabyte for non-EU travelers.
SM-DP+
Subscription Manager Data Preparation Plus
The server that delivers eSIM activation profiles. When your phone scans a QR code, it contacts the SM-DP+ server encoded in the QR, downloads the profile, and installs it.
top-up
add data to an existing eSIM
The action of buying another data plan that extends an already-installed eSIM — no new QR, no new install. The same eSIM profile gets a fresh data allowance.
WiFi calling
phone calls over WiFi
A feature where your phone routes calls through WiFi instead of the cellular network. Useful when cell coverage is weak but WiFi is strong (hotels, home, etc.).