Short, plain-English definitions for every term you might run into on this site or when researching phone unlocking. Where a term has its own full guide, we link to it.
Identifiers
IMEI — International Mobile Equipment Identity. A 15-digit number identifying one physical device. See what is an IMEI.
IMEI2 — the second IMEI on a dual-SIM or eSIM phone, one per SIM slot or profile.
ICCID — the unique number printed on a SIM card itself. Different from an IMEI: the ICCID identifies the SIM, the IMEI identifies the phone.
ESN — Electronic Serial Number. An older identifier used mainly on CDMA-era networks before IMEI became the standard almost everywhere.
Locks & restrictions
Carrier lock / network lock — a restriction tied to one network that blocks other SIM cards from working. See carrier-locked vs. unlocked phones.
Unlocked phone — a phone that accepts a SIM from any compatible carrier.
iCloud Activation Lock — an Apple account-level lock tied to Find My. Independent of carrier lock status. See iCloud/FRP locks vs. carrier locks.
FRP (Factory Reset Protection) — the Android/Google equivalent of Activation Lock, requiring the previous Google account after a factory reset.
Bootloader lock — a separate, device-level restriction on installing custom firmware. Unrelated to carrier locks and not something a carrier unlock touches.
Buying & selling
Blacklist — a shared industry record of phones reported lost, stolen, or left with an unpaid balance. A blacklisted phone generally cannot be activated on major networks. See checking a used phone's IMEI.
Clean IMEI — an IMEI with no blacklist flags against it.
EIP / financed phone — a phone still being paid off on an installment plan with a carrier. Usually must be paid in full before it can be unlocked.
GSMA — the industry association whose shared databases underpin how IMEIs are recognized and blacklisted across participating carriers worldwide.
Reactivation lock — Samsung's own account-level lock (via Find My Mobile), functioning much like Apple's iCloud Activation Lock but for Galaxy devices.
Connectivity
eSIM — a digital SIM profile built into the phone, used instead of (or alongside) a physical SIM card. See using your phone abroad.
Dual SIM — a phone that can hold two active lines at once, whether two physical SIMs, one physical plus one eSIM, or two eSIMs depending on the model.
Band compatibility — whether a phone's radio hardware supports the specific frequencies a given network uses. Being unlocked does not guarantee band compatibility.
MVNO — Mobile Virtual Network Operator. A carrier brand that runs on another network's towers rather than owning its own.
Roaming — using your home carrier's service while physically on another network's coverage, typically at a premium rate.
APN — Access Point Name. Settings that tell a phone how to connect to a specific carrier's data network — occasionally needs to be entered manually with a new SIM.
The unlock itself
Network unlock / permanent unlock — an official, carrier- or manufacturer-recognized change that removes a carrier restriction for good. See how carrier unlocking works.
Temporary / soft unlock — an unofficial workaround, not something this site offers, that can revert after a software update or reset.
Unlock code — a short numeric code some carriers issue that you enter on the device itself, once, the first time it detects a different network's SIM. See unlocking a Samsung Galaxy phone for an example.
Remote unlock — an unlock applied against the IMEI with nothing to type on the phone, as opposed to a code-entry unlock.
Accounts & plans
Prepaid — a plan paid for in advance, with no fixed contract term. Prepaid phones can still carry a carrier lock, just under different rules than postpaid.
Postpaid — a plan billed after usage, typically tied to a contract or device installment plan, which is the most common reason a phone is locked in the first place.
Porting — transferring your existing phone number to a new carrier. Independent of carrier lock status, though you'll need an unlocked phone to actually use that new carrier's SIM.
Carrier branding — a carrier's own logo, boot screen, or pre-installed apps on a phone it sold. Cosmetic, and separate from whether the phone is locked.
