To solve this question, the user needs to have knowledge about serialization. Serialization is the process of converting an object into a stream of bytes or characters, which can be stored or transmitted over a network.

Option A is correct. Serialization involves converting objects to byte streams, which can be easily transmitted over a network or stored in a file.

Option B is incorrect because serialization does not involve converting objects to strings. Although strings can be used to represent serialized data, they are not the same thing as serialization.

Option C is incorrect because serialization does not involve converting objects to Unicode characters. Unicode is a character encoding scheme that allows characters from different languages to be represented in a consistent manner. However, it is not directly related to serialization.

Option D is incorrect because serialization is a real concept that involves converting objects to byte streams or character streams.

Therefore, the correct answer is: A. Converting objects to byte stream.