verschlossen
locked
Secured by a lock or bolt so that it cannot be opened; locked shut.
Die Tür zum Archiv war fest verschlossen.
The door to the archive was firmly locked.

locked / reserved
Loading your saved state.
locked
Secured by a lock or bolt so that it cannot be opened; locked shut.
Die Tür zum Archiv war fest verschlossen.
The door to the archive was firmly locked.

'Verschlossen' is the past participle of the verb 'verschließen' (to lock, to bolt). Here it is used as an adjective to describe a state.
Der Briefumschlag war bereits fest verschlossen.
The envelope was already firmly sealed.
The meaning is easy to recognize from the subject. If 'verschlossen' refers to an object (door, box, bottle), it means 'zugesperrt' (locked). If it refers to a person, it means 'introvertiert' (introverted) or 'zurückhaltend' (reserved).
Die Schatzkiste war seit Jahrhunderten verschlossen.
The treasure chest had been locked for centuries.
The meaning 'introvertiert' (introverted) is a metaphor. A reserved person is like a locked door: they do not let anyone in to see their thoughts or feelings.
Er wirkt oft verschlossen, aber eigentlich ist er nur schüchtern.
He often seems reserved, but actually he is just shy.
open
'offen' and 'verschlossen' are opposites in important meanings. With doors, windows, or containers, 'offen' means that they are not closed; 'verschlossen' means that they are locked or secured. With people, 'offen' means that someone speaks honestly and directly. 'verschlossen', on the other hand, describes someone who says little about their thoughts or feelings. The words can be confusing because both can be used for things as well as for people. So pay attention to whether it is about an object or about a person's behavior.

Nach dem Streit war Tom sehr verschlossen und sprach kaum noch.
After the argument, Tom was very reserved and hardly spoke anymore.
Beim Lüften bleibt das Fenster zehn Minuten offen.
When airing the room, the window stays open for ten minutes.