What is a byte array?

Is not unique to Unity, although it has some specific utilities, it could not even talk about Unity but in each case that Unity uses.

Like any array, it is a sequence of data of a certain type, and in this case it is a simple byte. You can put whatever you want there. Virtually you can put any information in a byte[] because any data is a string of bytes. It can be a text, an executable, an image, a video, a sound, any pattern, something with a specific format, it does not matter.

Some objects can be generated or stored generically as a array of bytes. Example:

using UnityEngine;

public class ExampleScript : MonoBehaviour {
    public void Start() {
        // Create a 16x16 texture with PVRTC RGBA4 format
        // and fill it with raw PVRTC bytes.
        Texture2D tex = new Texture2D(16, 16, TextureFormat.PVRTC_RGBA4, false);
        // Raw PVRTC4 data for a 16x16 texture. This format is four bits
        // per pixel, so data should be 16*16/2=128 bytes in size.
        // Texture that is encoded here is mostly green with some angular
        // blue and red lines.
        byte[] pvrtcBytes = new byte[] {
            0x30, 0x32, 0x32, 0x32, 0xe7, 0x30, 0xaa, 0x7f, 0x32, 0x32, 0x32, 0x32, 0xf9, 0x40, 0xbc, 0x7f,
            0x03, 0x03, 0x03, 0x03, 0xf6, 0x30, 0x02, 0x05, 0x03, 0x03, 0x03, 0x03, 0xf4, 0x30, 0x03, 0x06,
            0x32, 0x32, 0x32, 0x32, 0xf7, 0x40, 0xaa, 0x7f, 0x32, 0xf2, 0x02, 0xa8, 0xe7, 0x30, 0xff, 0xff,
            0x03, 0x03, 0x03, 0xff, 0xe6, 0x40, 0x00, 0x0f, 0x00, 0xff, 0x00, 0xaa, 0xe9, 0x40, 0x9f, 0xff,
            0x5b, 0x03, 0x03, 0x03, 0xca, 0x6a, 0x0f, 0x30, 0x03, 0x03, 0x03, 0xff, 0xca, 0x68, 0x0f, 0x30,
            0xaa, 0x94, 0x90, 0x40, 0xba, 0x5b, 0xaf, 0x68, 0x40, 0x00, 0x00, 0xff, 0xca, 0x58, 0x0f, 0x20,
            0x00, 0x00, 0x00, 0xff, 0xe6, 0x40, 0x01, 0x2c, 0x00, 0xff, 0x00, 0xaa, 0xdb, 0x41, 0xff, 0xff,
            0x00, 0x00, 0x00, 0xff, 0xe8, 0x40, 0x01, 0x1c, 0x00, 0xff, 0x00, 0xaa, 0xbb, 0x40, 0xff, 0xff,
        };
        // Load data into the texture and upload it to the GPU.
        tex.LoadRawTextureData(pvrtcBytes);
        tex.Apply();
        // Assign texture to renderer's material.
        GetComponent<Renderer>().material.mainTexture = tex;
    }
}

I put on GitHub for future reference.

Source .

This example mounts an image pattern that will create a texture object to use in game scene objects. These bytes end up, forming a drawing form of somehow, they indicate where it should have a certain color tone to simulate a hypothetical surface. In a real code could go changing these numbers, which were written in hexadecimal notation, but are number like any other can go from 0 to 255, and after changing you can see changes in the texture that is applied to the game. A texture is a string of bytes .