To take in has various meanings depending on the context:
Absorb or assimilate information, knowledge, or ideas: She was trying to take in all the details of the presentation.
Accept and provide home or accommodation: They decided to take in a foreign exchange student.
Perceive and comprehend ones surroundings through sight: He stopped for a moment to take in the stunning view.
To understand or believe something: It took a while for the news to be taken in.
Adjust a garment to make it narrower or tighter: She had to take in the dress because it was too loose.
So, the general definition could be to receive, absorb and/or comprehend something intellectually, visually or physically.