what is a tcp packet?

if your firewall blocks an outgoing tcp packet,what exactly is it blocking?

and what info can be gained through a tcp packet?

http://computer.howstuffworks.com/question525.htm

http://www.networksorcery.com/enp/protocol/tcp.htm

a packet's a unit of data sent across the network. let's say for example, you order a large computer desk from ebay. the seller disassembles it, and ships the parts to you in boxes. when you receive it, you reassemble the desk. same thing with a packet, in this case, the boxes would be the packets. the header (or label) of the packet would be the equivalent to the shipping address on the shipped box

the reason TCP/IP converts large data files into smaller chunks, for sending over a network, is so that less data will have to be re-transmitted if errors occur.

thanks guys!