Lunch is the meal that takes place in the middle of the day. 'Lunch' refers both to the meal which is had at this time, and the time itself. 'Lets do lunch', for example, suggests either eating together at this time of the day, or spending the time of the day when other people are eating, doing something else - like deciding the fates of business empires, and so on.
Often, the quality of your lunch depends more on location than price. Sandwiches - normally a popular choice as part of a lunch meal, because of their portability: you can bring them from home to work, which saves you having to buy commercially pre-prepared food at lunch time - if purchased at any train station are likely to be dry, rubbery, and generally better suited to being a brake pad for a car, regardless of cost. On the other hand, a sandwich made by your mother when you are ten years old and playing outside during a summer vacation is likely to be one of the best sandwiches you have ever had.
However, even worse than a sandwich purchased in a train station is a 'gourmet' meal served in coach class1 on an airline. This will consist, if you are lucky, of the following:
A sandwich similar to one found in a train station, but smaller.
A badly bruised apple, possibly with a worm in it.
A small, unsatisfying bag of honey-mustard pretzel bits, each hard enough to support the weight of the airplane you are sitting in, as well as being so salty you're almost considering buying the US$5 shot glass of stale soda they have been offering you.
A spork*, for no particular purpose.
On the other hand, a lunch can be a very pleasurable and useful experience. Many important decisions are made over lunch and taking a lunch break can get you out of doing nearly any job for the next hour. A good lunch is a thing to look forward to, a break in the middle of the day, a way to separate the period of the morning when you are still finishing your coffee from the time of day when work actually gets done.
In fact, many cultures believe lunch to be the most important meal of the day. Amongst them are the people of Mexico. Mexicans take lunch very seriously, spending two or three hours in the afternoon for a lunch break, including a sleep and some serious time for digestion. In fact, in Mexico most stores close down from around 1pm-2.30pm so that everyone can have a nice long lunch break. Sadly, in an effort to conform to modern business practices, many large companies in Mexico and other pro-long lunch break countries have been trying to cut back on the practice of extended lunches.