TCP Window Full

This question has been asked several times before. This is TCP flow control in action. From Section 1.5 of RFC 793:

Flow Control:
TCP provides a means for the receiver to govern the amount of data
sent by the sender.  This is achieved by returning a "window" with
every ACK indicating a range of acceptable sequence numbers beyond
the last segment successfully received.  The window indicates an
allowed number of octets that the sender may transmit before
receiving further permission.

In a nutshell, the receiver’s receive buffer is full. For more details, read the RFC and/or the answers to these other questions:

• http://ask.wireshark.org/questions/12474/why-am-i-seeing-tcp-window-full-on-upload
• http://ask.wireshark.org/questions/4610/tcp-window-full
• http://ask.wireshark.org/questions/2365/tcp-window-size-and-scaling
• http://ask.wireshark.org/questions/22090/the-transmission-window-is-now-completely-full
• …

Or try a basic google search.