The honor system is a philosophical way of running a variety of endeavors based on trust and honor. Something that operates under the rule of the "honor system" is usually something that does not have strictly enforced rules behind its functioning. In the UK, it would more often be called a "trust system" and should not be confused with the British honours system.
A person engaged in a honor system has strong negative connotations associated with breaking or going against it. The negatives may include things like community shame, loss of stature, or in extreme situations, banishment....
In some places, public transportation such as trains operate on an honor system. The local government may find it impractical or overly expensive to install ticket-checking turnstiles at every station, and instead rely on casual human surveillance to check if all train riders possess tickets. In such a system one could thus ride the train without paying, and simply hope to be lucky enough to avoid a random ticket check during the trip. Though unethical, such behavior is impossible for an honor system by itself to prevent, although the behavior can be reduced by enforcing penalties for those who choose to cheat the system.
Some hotels in continental Europe operate an honor bar, allowing guests to serve and record their own drinks and saving the cost of a night bartender. Patrons could theoretically lie about their drink consumption, and the hotel would have only limited powers to verify their claims. The concept of hotel "mini bars" in the United States is similar.
Many publicly funded museums and art galleries around the world ask for a certain "suggested" or "minimum" donation in exchange for admission. Patrons are almost never supervised during their donations, so there is no way of making sure the suggested minimum is being paid.
In some colleges, the honor system is used to administer tests unsupervised. Students are generally asked to sign an honor code statement that says they will not cheat or use unauthorized resources when taking the test. As an example, at the Washington & Lee University a student taking an examination is required to sign, date and include the following pledge: "On my honor as a student I have neither given nor received aid on this examination." There is but one penalty for transgression of the honor code, and that is dismissal from the University.
Another example can be seen in fundraising drives. Many charities distribute boxes of confectionery to businesses, which are placed in waiting rooms or similar for people to purchase items from. The confectionery is free to be removed by anyone who wishes to take it, and there is no enforcing of payment other than through the expectation of honesty. Indeed, most such boxes of confectionery bear the comment 'Your honesty is appreciated' near where money is deposited....