"Safewords" are a security feature of TF2WH where you get a generated unique 2 word combination. Remember this word and keep it a secret because only you and TF2WH know this word. When a bot opens a chat to you, it will tell you the safeword so that you know you're talking to an official bot, and not a scammer.
When you first visit the website a safe word will be generated for you, you will see a display similar to this:
From then on, your safeword will appear above your chat box on the site, and if you're not happy with the one you have, or believe it may have become compromised, you can generate a new one by clicking the "reload" icon beside the safeword.
If you are trading with a TF2WH bot and it does not give you a safeword or the safeword it gives you is not the correct word, then you are probably talking to a SCAMMER! DO NOT TRADE! Check your safe word on the website and the chat log underneath to make sure.
If you are trading with a scammer, take note of their SteamID, get a screenshot, and check at SteamRep.com to see if they have already been reported as a scammer, if they haven't, post your evidence and get that scammer banned.