Compressor is a TIdZLibCompressorBase property that represents the ZLib compression library object for use for HTTP responses having "deflate" or "gzip" encoding for its content. Compressor is used, when assigned, when reading an HTTP response with the desired ContentEncoding in Response. 

Applications must assign a TIdZLibCompressorBase (or descendant) class instance to the property to allow decoding of the content stream for the HTTP response. When Compressor is unassigned, the content stream for the response remains in its encoded content transfer encoding. 

Compressor is not available on the .Net platform.

TIdZLibCompressorBase 

TIdHTTPResponse