ALARP ("as low as reasonably practicable"), or ALARA ("as low as reasonably achievable"), is a principle in the regulation and management of safety-critical and safety-involved systems.

Albedo is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that reflects all incident radiation.

A hand-held electrically operated signal lamp.

Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils.

An arrangement of different structural members in one straight line: alignment of butt welds, alignment of stiffeners, etc. Many ships have suffered when other design requirements have been assigned undue priority over structural alignment.

A type of primary battery which derives its energy from the reaction between zinc metal and manganese dioxide.

One of the most developed fuel cell technologies.

In chemistry, an alkene is a hydrocarbon that contains a carbon–carbon double bond.

A synthetic resin made by a reaction of two chemicals in the presence of natural or processed oil.

In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins.

A battery electric vehicle or all-electric vehicle is a type of electric vehicle (EV) that exclusively uses chemical energy stored in rechargeable battery packs, with no secondary source of propulsion.

Any corridor aboard vessel connecting one part of the accommodation to another part.

The act of striking or collision of a moving vessel against a stationary object.

Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.

An alloy is an admixture of metals, or a metal combined with one or more other elements.

A flux which the alloy content of the weld metal is largely dependent on.

A test specimen with the reduced section composed entirely of weld metal.

Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.

Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus.

Alpine climate is the typical weather (climate) for the regions above the tree line.