An odd job is an informal method of irregular employment, usually manual or menial unskilled work. Odd jobs are often temporary and short term, picked up to supplement income. An odd job differs from temporary employment in that there is usually no contract between parties, and pay is given under the table. Sometimes pay is skipped entirely in favor of a barter. Odd jobs are classified as part of the informal economy.
A simple example of an odd job is paying your neighbor to mow your lawn for $20. This can be extended into mowing the lawn every two weeks, or maybe giving him beer in instead of money. Or perhaps the neighbor's kid is mowing the lawn instead, thus gently circumventing child labor laws in order for the kid to gain some extra money. A classic cliche odd job is washing dishes at a restaurant when you can't pay for your meal.
Odd jobs take place at all levels of an economic structure, but employment is always voluntary between the two parties. Odd jobs also take place in both rural and urban settings, with jobs ranging from manual labor to data entry. Some people will string together a bunch of odd jobs, or perhaps be available to several parties at once in order to produce a regular stream of income.