
blockieren
to block
To physically block a path, road, or entrance so that no one can pass through.
Ein umgestürzter Baum blockiert die gesamte Fahrbahn.
A fallen tree is blocking the entire roadway.
to block
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to block
To physically block a path, road, or entrance so that no one can pass through.
Ein umgestürzter Baum blockiert die gesamte Fahrbahn.
A fallen tree is blocking the entire roadway.

to block
To actively prevent or stop the functioning of a system, the execution of an action, or a process.
Die Opposition versucht, das neue Gesetz im Parlament zu blockieren.
The opposition is trying to block the new law in parliament.

to block / reserve
To reserve something (e.g., an appointment, a room, a seat) for a specific time or person so that it is not available to others.
Können Sie mir diesen Konferenzraum für morgen Vormittag blockieren?
Can you block this conference room for me for tomorrow morning?

to freeze up
To be so mentally inhibited in a situation that you can no longer think clearly or act.
Immer wenn der Prüfer eine Frage stellte, habe ich komplett blockiert.
Whenever the examiner asked a question, I completely froze up.
'Blockieren' is a verb ending in '-ieren' that comes from an international word stem. These verbs are always regular, not separable, and form the past participle with '-iert' ('blockiert').
Er hat den Parkplatz für seinen Chef blockiert.
He blocked the parking space for his boss.
The meaning of 'blockieren' becomes clear from the object. Physical things like 'Straße' (street) or 'Tür' (door) are blocked. Abstract things like 'Gesetz' (law) or 'Prozess' (process) are prevented. Appointments or resources are reserved.
Die Demonstranten blockierten die Brücke für mehrere Stunden.
The demonstrators blocked the bridge for several hours.
Only in the meaning of being mentally inhibited is 'blockieren' used without an accusative object. It then describes the state of the person who is acting—or rather, cannot act.
Ich war so nervös, dass ich bei der mündlichen Prüfung komplett blockiert habe.
I was so nervous that I completely froze up during the oral exam.
The meaning 'reservieren' (to reserve) is mainly used in colloquial language or everyday office contexts. It is an informal way to express that you are setting something aside for yourself or others.
Kannst du den Nachmittag in meinem Kalender für unser Projekt blockieren?
Can you block the afternoon in my calendar for our project?
to prevent
Both verbs can refer to stopping a process. Verhindern emphasizes that an event or result does not happen at all, while blockieren tends to mean hindering the process or execution. When the focus is on the event not taking place, verhindern is appropriate; for a stopped process, use blockieren.

Ein technischer Fehler blockierte den Start der Maschine.
A technical fault blocked the machine from starting.
Die Sicherheitsprüfung verhinderte den Start der Maschine.
The safety inspection prevented the machine from starting.