
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
Loading your saved state.

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?

to be possible
Colloquial for being possible or included in the budget.
Ein neuer Fernseher ist dieses Jahr finanziell leider nicht drin.
A new TV unfortunately isn't financially possible this year.

to be into
Colloquial for being well informed about or involved in a topic or subject matter.
Wenn du Fragen zur neuen Software hast, frag Alex, der ist da voll drin.
If you have questions about the new software, ask Alex—he's totally into it.
'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.
in it / therein
Darin and drin can both express that something is inside a container that has been mentioned. Darin is neutral and refers more clearly to the container; drin is the colloquial short form and is especially suitable in casual conversation.

Mach die Schachtel auf, denn der Schlüssel ist drin.
Open the box because the key is inside.
Die Schachtel ist verschlossen, und der Schlüssel liegt darin.
The box is locked, and the key is inside it.