what does it mean followed by the pound key

It means the # symbol, usually on a phone keypad. In many systems, “followed by the pound key” means press the number or code first, then press # to confirm or finish entry.

What it usually means

• On phones, the pound key is the # button.

• In automated phone menus, it often tells the system you’re done entering digits.

• In texting and online use, the same symbol is often called a hashtag.

Example

If a recording says, “Enter your account number followed by the pound key,” you would type the account number and then press #.

Different names

People may call # the pound key, hash key, number sign, or octothorpe depending on the region and context.

TL;DR: it usually means press # after the number or code.