Format
If a Transfer-Encoding field with a value of chunked is specified in an HTTP message (either a request sent by a client or the response from the server), the body of the message consists of an unspecified number of chunks, a terminating last-chunk, trailer, and a final CRLF sequence (i.e. carriage return followed by line feed).
Each chunk starts with the number of octets of the data it embeds expressed in hexadecimal followed by optional parameters (chunk extension) and a terminating CRLF sequence, followed by the chunk data. The chunk is terminated by CRLF. If chunk extensions are provided, the chunk size is terminated by a semicolon followed with the extension name and an optional equal sign and value.
The last-chunk is a regular chunk, with the exception that its length is zero.
The last-chunk is followed by the trailer, which consists of a (possibly empty) sequence of entity header fields. Normally, such header fields would be sent in the message's header; however, it may be more efficient to determine them after processing the entire message entity. In that case, it is useful to send those headers in the trailer.
Headers that regulate the use of trailers are TE (used in requests), and Trailers (used in responses).
Read more about this topic: Chunked Transfer Encoding