Cub Cadet XT1 Enduro LT 42 in. 18 HP Kohler 5400 Series Engine Hydrostatic Drive Gas Riding Lawn

Eighteen or 18 may refer to:

• 18 (number), the natural number following 17 and preceding 19
• one of the years 18 BC, AD 18, 1918, 2018

A cadet is a student or trainee, and is typically used in military settings to denote an individual undergoing training to become commissioned officers. Several civilian organisations, including civil aviation groups, maritime organisations, and police services, also designate their trainees as cadets.

A cub is the young of certain large predatory animals, such as big cats and bears.

Cub or CUB may also refer to:

Enduro is a form of motorcycle sport run on extended cross-country, off-road courses. Enduro consists of many different obstacles and challenges. The main type of enduro event, and the format to which the World Enduro Championship is run, is a time-card enduro, whereby a number of stages are raced in a time trial against the clock.

An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.

Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power generation), heat energy (e.g. geothermal), chemical energy, electric potential and nuclear energy (from nuclear fission or nuclear fusion). Many of these processes generate heat as an intermediate energy form, so heat engines have special importance. Some natural processes, such as atmospheric convection cells convert environmental heat into motion (e.g. in the form of rising air currents). Mechanical energy is of particular importance in transportation, but also plays a role in many industrial processes such as cutting, grinding, crushing, and mixing.

Mechanical heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a mechanical heat engine, in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Unlike internal combustion engines, a reaction engine (such as a jet engine) produces thrust by expelling reaction mass, in accordance with Newton's third law of motion.

Apart from heat engines, electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion (a chemical engine, but not a heat engine).

Chemical heat engines which employ air (ambient atmospheric gas) as a part of the fuel reaction are regarded as airbreathing engines. Chemical heat engines designed to operate outside of Earth's atmosphere (e.g. rockets, deeply submerged submarines) need to carry an additional fuel component called the oxidizer (although there exist super-oxidizers suitable for use in rockets, such as fluorine, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means of nuclear reactions.

Gas is one of the four fundamental states of matter. The others are solid, liquid, and plasma. A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes gases from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer.

The gaseous state of matter occurs between the liquid and plasma states, the latter of which provides the upper-temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention. High-density atomic gases super-cooled to very low temperatures are classified by their statistical behavior as either Bose gases or Fermi gases. For a comprehensive listing of these exotic states of matter, see list of states of matter.

Kohler is an occupational surname of German origin. It means "charcoal burner". Notable people with the surname include:

• Alan Kohler, Australian journalist
• Anton Kohler, German chess player
• Berthold Kohler (born 1961), German journalist
• Charles-Amédée Kohler (1790–1874), Swiss chocolate maker
• Ernesto Kohler (1849–1907), flautist and composer
• Fred Kohler, American actor
• Josef Kohler, German jurist
• Juliane Köhler, German actress
• Jürgen Kohler, former German football player
• Kaufmann Kohler (1843–1926), Reform rabbi
• Klaus J. Kohler, German phonetician
• Max J. Kohler, American lawyer
• Richie Kohler, shipwreck diver and historian
• Sheila Kohler, South African writer
• Peter Kohler, American writer, historian and philanthropist

A lawn () is an area of soil-covered land planted with grasses and other durable plants such as clover which are maintained at a short height with a lawn mower (or sometimes grazing animals) and used for aesthetic and recreational purposes—it is also commonly referred to as part of a garden. Lawns are usually composed only of grass species, subject to weed and pest control, maintained in a green color (e.g., by watering), and are regularly mowed to ensure an acceptable length. Lawns are used around houses, apartments, commercial buildings and offices. Many city parks also have large lawn areas. In recreational contexts, the specialised names turf, pitch, field or green may be used, depending on the sport and the continent.

The term "lawn", referring to a managed grass space, dates to at least the 16th century. With suburban expansion, the lawn has become culturally ingrained in some areas of the world as part of the desired household aesthetic. However, awareness of the negative environmental impact of this ideal is growing. In some jurisdictions where there are water shortages, local government authorities are encouraging alternatives to lawns to reduce water use. Researchers in the United States have noted that suburban lawns are "biological deserts" that are contributing to a "continental-scale ecological homogenization." Lawn maintenance practices also cause biodiversity loss in surrounding areas.