die Laufzeit
term
The fixed period for which a contract, agreement, or financial product (e.g., a loan) is valid.
Mein Handyvertrag hat eine Mindestlaufzeit von 24 Monaten.
My mobile phone contract has a minimum term of 24 months.

runtime / term
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term
The fixed period for which a contract, agreement, or financial product (e.g., a loan) is valid.
Mein Handyvertrag hat eine Mindestlaufzeit von 24 Monaten.
My mobile phone contract has a minimum term of 24 months.

The word consists of 'Lauf' (from the verb 'laufen' — to run) and 'Zeit' (time). It literally describes the time during which something 'läuft' (runs), meaning it is active, valid, or moving. This basic idea connects all meanings.
Die lange Laufzeit des Akkus war ein wichtiges Kaufargument.
The long battery life was an important selling point.
In all meanings, 'Laufzeit' (runtime/term) is very often used with the verbs 'haben' (to have) or 'betragen' (to amount to/be) to indicate duration.
Der Kredit hat eine Laufzeit von zehn Jahren.
The loan has a term of ten years.
When it is about contracts, loans, or subscriptions, this meaning is intended. Signal words here are 'Monate' (months), 'Jahre' (years), 'kündigen' (to cancel), or 'verlängern' (to extend).
Ich habe die Laufzeit meines Abonnements um ein weiteres Jahr verlängert.
I extended the term of my subscription by another year.
In connection with films, series, podcasts, or plays, 'Laufzeit' (runtime) describes the duration of the performance or screening. Signal words here are 'Minuten' (minutes), 'Stunden' (hours), or the name of the medium itself.
Die erste Folge der Serie hat eine Laufzeit von 55 Minuten.
The first episode of the series has a runtime of 55 minutes.
When it is about technical devices, it usually refers to 'Akku-Laufzeit' (battery life), meaning how long a device works without being connected to power. The duration of a computer process can also be described this way.
Die Akku-Laufzeit meines neuen Handys ist beeindruckend.
The battery life of my new phone is impressive.
This meaning of 'Laufzeit' (travel time) is used almost exclusively in technical or physics-related specialist contexts, for example when measuring signals (GPS, radar) or sound waves.
Aus der Laufzeit des Echos kann man die Entfernung zum Hindernis berechnen.
The distance to the obstacle can be calculated from the travel time of the echo.
length
'die Länge' and 'die Laufzeit' can both describe a duration in time. 'die Länge' is more general and fits, for example, with a film, a conversation, or a text. 'die Laufzeit' is used more when a period of time is fixed or something runs for a certain time: a contract, a loan, a program, an exhibition, or a film. The words can be confused with films because both are possible. In contracts or technology, however, 'Laufzeit' sounds more precise and natural.

Die Laufzeit des neuen Handyvertrags beträgt zwei Jahre.
The term of the new mobile phone contract is two years.
Am Morgen spricht die Fahrerin über die Länge der Pause.
In the morning, the driver talks about the length of the break.