adjective
secret, confidential
B1
Geheim means 'secret' or 'confidential'. It's an adjective, gradable: comparative geheimer, superlative am geheimsten. Used attributively and predicatively (die geheime Nachricht, etwas ist geheim). Not reflexive; no specific preposition. Contrast with 'heimlich' (more like covert). Common in security and privacy contexts.
Examples
Der Minister sagte, dass die Informationen geheim blieben, bis die Ermittlungen abgeschlossen waren.
The minister said that the information remained secret until the investigations were completed.
Die Informationen sind geheim und dürfen nicht geteilt werden.
The information is confidential and must not be shared.
Der Plan ist streng geheim.
The plan is top secret.
Details
Mnemonics
Picture a locked chest with a big label 'geheim' (secret) on it.
Sounds like 'guy-hime' — imagine a man hiding something secret.
Notes
Commonly used attributively and predicatively. Comparative: geheimer, superlative: am geheimsten.