EOL is a single byte used at the end of the options. To see an example, open the Flow312.pcap packet capture, put tcp.option_kind == 0 in the display filter, and press Enter. Wireshark will display frame 2. Expand the TCP header options, which will show the EOL at the end of the list:
Flows312 frame 2 options list
Another TCP option is NOP, which isn't an option at all, but a placeholder, as we'll see next.