Bytes are a unit used to measure information or data on digital devices. The bytes format of xff xff xff is a combination of three bytes, represented in hexadecimal notation.
In this case, the format xff xff xff is interpreted as three bytes where each byte has a value of 0xFF. This can be also interpreted as a 24-bit integer of hexadecimal 0xFFFFFF, representing the maximum value that a 24-bit integer can contain. In decimal, this would translate to 16,777,215.
Additionally, this format is used in a few different ways. It can be used in a data structure to indicate a given field is not used or to denote a value indicating an ‘unknown’. It is also used in HTML to define the color white, as displayed in the following sample code: <body bgcolor="#FFFFFF">.
Hope this helps!