• Shell = The "command line". (More specifically, the part of the command-line interface that prompts you for commands, runs commands, and interfaces with the underlying OS.)
• TUI = Terminal User Interface, a basic text-based interface that typically uses a text terminal as a grid of characters
• Reverse Shell = A way of getting a terminal/command line on a remote system, especially when that remote system is not directly accessible on the Internet
• Flimsy Reverse Shell = A reverse shell heavily limited by bandwidth, latency, reliability, or other restrictions. Makes using it a pain.
• ^C = Abbreviation for Ctrl-C. Usually used to kill the currently running command in a terminal.
• netcat = A command that is able to connect and receive connections and perform basic data transmission. Can be used to establish a rudimentary reverse shell.

Explanation:

Most work using commands on terminals is very low-bandwidth, so is particularly well-suited to slow or unreliable connections. However, programs that offer a terminal-based UI often use far more bandwidth (and other resources) in sending UI updates over a terminal. Sometimes, an overly aggressive terminal UI can send so many updates over a slow connection that the connection just gets "frozen" waiting for all that data. If one accidentally does this, the usual response is to try to kill the program sending data ASAP to limit the amount of time spent waiting to receive it; typically by smashing Ctrl-C repeatedly until it stops. However, the netcat program itself (unlike proper remote terminal commands like SSH and telnet) will intercept the Ctrl-C and will exit itself; in this example, ending the remote shell.