Binary-data is information stored using a two character alphabet (typically written using 0 and 1)
Binary Data is information which is stored using a two character alphabet. For example, the number 42 could be stored as its base-2 representation: 101010.
In modern computers, almost all data is ultimately represented in binary form.
To be useful, the writer and reader of binary data must have a pre-agreed format (e.g. a file consisting of a 32-bit, two's compliment integer followed by three IEEE 754 floating point numbers).
The term is usually used to distinguish data stored in this way against data stored using a textual encoding. For example, the digits of 42 in base-10 (4 and 2) may be represented using ASCII as 00110100 and 00110010. Whether this is considered binary data or not depends on the task at hand; a chat client would consider messages as textual data, but the communication protocol it is built on may consider the same messages as arbitrary binary data.
