What does 民以食为天 mean?

the original from that 王者以民人为天，而民人以食为天 (The king takes the people as heaven, and the people take food as heaven).

means that the king regard people as the foundation of the country, people regard food as the foundation of life.

the masses regard food as their heaven—food is the first necessity of the people.
_{cchatty dictionary}

民以食为天mín yǐ shí wéi tiān

1. 食 means food, eat Also refers to food and suggested operation production resources required for food, etc
2. 天 means the sky, and god The most important thing to the survival of metaphor.
3. The people with food for their own lives, extended to the people life necessities such as food production resources are needed to survive.

As an emperor in ancient China, if you don't let your people have enough food to eat, they will rebel against you. So '民以食为天' means in order to rule people, you must let them have the food to eat and this is very important to your rule.

天 here means very important.

Another example of 天 is 人命关天 which means a person's life is very important/valuable.

I want to add to the answers above because I don't think they cover the full extent to the use of this saying.

This saying points out the respect that Chinese people have in their culture for food and its importance to the Chinese people.

Even in recent history, only two generations ago, many people died from hunger and this has had an effect on modern culture. Phrases such as "吃了吗" as a greeting also point to this.

This is apparent in many aspects of the culture; inviting others out to eat 请客, bringing out snacks and food as soon as a guest arrives, the complexity of preperation in Chinese cuisine and giving of health food gifts to others.

This is more than just saying food is the most important, it makes a vital point about the culture.

Sustenance is of utmost importance to the people.

The idiom where it was taken from, actually means that the wellbeing of his people should be of utmost concern to a ruler, and this concern is best addressed by keeping his people well fed.

First, as fefe said, this idiom should be “民以食为(wéi)天" and it comes from 《汉书·郦食其传》“王者以民为天，而民以食为天。” (biography of 郦食其 in the historical record of 汉 dynasty). That sentence means "People are the most important to an emperor, while foods are the most important to the people". Note that the correct pronunciation of the name is: lì yī jī

Why? Remember in ancient times, foods were not as sufficient as they are now (remember, even now some people in poverty are hungry all days), and foods are indispensable to the life.

Edit: More details

After reading that biography, I could explain more about the source. The context when 郦 spoke this was during the war time of 楚汉争霸, when he persuaded 刘邦 to occupy a city in which a lot of foods were stored. He spoke that to emphasize the importance of the foods (especially in the war time, if you don't have enough food supply, the soldiers won't fight for you, or even they would fight against you!)

Today, we usually use this proverb as an introduction sentence, when talking on the topic of foods. You would probably hear a sentence like this one from the host on the TV:

俗话说，“民以食为天”。今天，就让我给观众朋友们介绍几家以其特色菜闻名的餐馆吧。

It is popularly said that "foods are the most important to people". Now, please let me introduce you some restaurants famous for their featured dishes.