drin
inside
Colloquial short form of 'darin' (in it/inside it); indicates that something is located inside something.
Schau mal in die Schachtel, was ist da drin?
Look in the box—what's inside?

inside / possible
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inside
Colloquial short form of 'darin' (in it/inside it); indicates that something is located inside something.
Schau mal in die Schachtel, was ist da drin?
Look in the box—what's inside?

'Drin' (inside/in it) is the colloquial and very common short form of 'darin' (in it/inside it). In written and formal language, you should generally use 'darin' instead.
Was ist in dieser Kiste drin?
What's inside this box?
In its literal meaning, 'drin' often appears at the end of a main clause or question. It emphasizes the position inside something.
Mach bitte die Tür zu, es ist kalt. Wir bleiben lieber drin.
Please close the door; it's cold. We'd rather stay inside.
The phrase 'etwas ist drin' (something is possible) means that something is possible or doable, often with reference to money or time. The negative 'ist nicht drin' (is not possible) is very common.
Eine Gehaltserhöhung ist dieses Jahr leider nicht drin.
A salary increase unfortunately isn't possible this year.
The colloquial phrase '(in einem Thema) drin sein' (to be into/up to speed on a topic) means to know a lot about something or to be deeply involved in it. It is often intensified with adverbs like 'voll' (totally) or 'tief' (deeply).
Er programmiert seit 10 Jahren, der ist da tief drin.
He's been programming for 10 years; he's deeply involved in it.
possible
'möglich' and 'drin' can both express that something is possible or doable. 'möglich' is neutral and fits almost any situation, including formal conversations. 'drin' in the phrase 'drin sein' is colloquial. It is often used when talking about time, money, plans, or chances, for example whether something still fits within the budget or schedule. 'möglich' sounds more precise and general; 'drin sein' sounds more relaxed and everyday.

Ein kurzer Besuch ist am Wochenende noch drin.
A short visit is still possible on the weekend.
Ein früherer Termin ist leider nicht möglich.
Unfortunately, an earlier appointment is not possible.