Tamper-evident describes a package built so that you can SEE if someone has opened it before you. Think of the plastic ring under a bottle cap that breaks when you first twist, the foil seal on a yoghurt pot, the sticker across a box that tears and cannot be put back neatly. All of these are tamper-evident.

Here is the part students miss: tamper-evident does not mean nobody can open it. It means nobody can open it secretly. The seal is not a lock; it is a witness. Compare tamper-proof or tamper-resistant, which claim the thing is hard to open at all. Companies mostly say tamper-evident precisely because they cannot honestly claim tamper-proof — you can cut into almost anything if you try.

The word is formal and belongs to packaging, medicine, food safety, elections, and computer security (a tamper-evident log records changes so you can tell if someone edited it). You will read it on labels and in news reports, not hear it in conversation. It is written with a hyphen and normally goes before the noun: a tamper-evident seal, tamper-evident packaging.