A banner screen is a configurable text “welcome” display from a network host system. The text generally provides system information, such as data about the operating system (OS) and service packs, software versions and web services.
Unconfigured banners display default information and may also present login screens, both of which make them a target of hackers in attacks called banner grabbing. A banner can also be crafted by an administrator as a custom message, which could be misinformation provided for the purposes of obfuscation or a straightforward warning message for hackers.
When using Telnet, for example, you use different ports to access different services:
SMTP: telnet ip_address 25
HTTP: telnet ip_address 80
POP3: telnet ip_address 110