Pre-workout simply means before the workout. The pre-workout meal is your meal before a workout. This meal should ensure optimal performance during the workout.
The important thing to consider here is what you eat and when you eat it leading into the workout. You should avoid large and hard-to-digest meals when eating shortly before training. Otherwise, your body will be busy digesting during the workout. Your blood will be pumped into your stomach and not into your muscles, so your muscles will not be supplied with sufficient nutrients and your training performance will decrease.
So just before training, avoid foods with a high fat content and long-chain carbohydrates. These would be heavy in your stomach. The situation is different if you eat such a meal at a longer distance from your workout. A larger meal several hours before training is no problem.
Shortly before your training session (about 30-45 min before) you should focus instead on easily digestible and quickly available nutrients. Here you should again focus on a combination of carbohydrates and proteins and avoid fats.
Examples of such a pre-workout meal are a protein shake and a banana or egg whites and rice cakes with jam/honey.
If you are on a diet and want to avoid carbohydrates before your workout, you should still make sure to consume quickly available proteins. This even applies if you like to train in the morning and do not eat breakfast beforehand.
Do not work out on an empty stomach. Feed your body at least some protein beforehand to maintain an anabolic state.