No, this is not about whether or not you use swear words in your speeches, though I assume that you don't. This tip is about choosing the right words for your speech. The important thing is whether the message that your audience hear is the one that you intend to convey. If, after your speech, you talk to members of your audience and hear yourself saying "that's not what I meant", then you have failed in your mission.
In short, you need to use language that -
* is clear
* supports your message
* is authentically yours
Clarity should not be a problem. There is no trade-off between short words and great speaking. In fact many of the most powerful messages have been delivered in the most simple language - "I have a dream..", "We will overcome.." "The lady's not for turning".
Using words that support your message is very important too. The recent turmoil in financial markets may have been addressed more quickly if US politicians had stopped discussing a "bail-out package" and started talking about a "rescue plan", as they did recently.
Lastly, being authentic is important for every speaker, in every speech. Try to avoid clichés. Make up your own comparisons, based on your own experiences. Tell your own stories. That's what people want to hear.