I saw a speaker define gout the other day. His head was focused on his notes on the lectern. The enitre audinece could have been making faces at him and the speaker would have never known.
When speaking one common mistake of the inexperienced is trying to give definitions. The challenge comes from not being able to remember the entire definition. To further add injury, the speaker will have to look down to read from the notes. This causes a total loss of audience contact.
To remedy this, consider picking up the notes and just read them. Your reading them anyway, why not just hold your notes up and maintain the contact with the audience.
An example of a long complicated definition would be to define gout as it was given recently. If it is unfamiliar or challenging information, reading will help enhance the quality of your speaking.