Topologist's sine curve

LD may refer to:

In science and mathematics:

• Lethal dose#, where "#" represents the percentage of test organisms killed by a specific dosage (of drugs, radiation, etc.), e.g. half will die at LD50
• The logarithm of base 2, $\mathrm{l}\mathrm{d}(x)={\log }_2(x)$, from the Latin logarithmus dualis
• Lunar distance (astronomy), the distance between the Earth and the Moon and a measure of navigation
• Linkage disequilibrium, when distinct alleles appear together more often than by chance (thanks to founder effects, etc.) in genetics
• lactate dehydrogenase, an enzyme in plants and animals
• London dispersion forces, weak intermolecular forces

In technology:

• Laser diode, semiconductor laser-emitting device
• Laserdisc format, an obsolete optical disc video/data format and predecessor to Digital Video Disc (DVD)
• ld (Unix), the linker command on Unix and Unix-like systems
• Long distance, a telephone call to another area sufficiently far away to be charged at a higher rate
• Loop Disconnect dialing
• ld, an instruction on a Z80 CPU
• Line Dubbed, a term for pirate copies with an audio track, which has been ripped from the line out connection of a projector
• Ladder diagram (disambiguation), various meanings
• Linz-Donawitz process, a widely used conversion process in steelmaking
• Linked data, a method of publishing structured data so that it can be interlinked and become more useful

In politics:

• Liberal democracy, a form of government based on rule of the people (democracy) tempered by the rule of law and natural rights (liberalism)
• A form of debate (Lincoln–Douglas debate)
• Liberal Democrats A UK-based liberal political party

In television:

• Lorraine "L.D." Delacorte, a character from the Degrassi series played by Amanda Cook
• Larry David, sometimes referred to as L.D. in the television show Curb Your Enthusiasm
• Latin Disciples, the name of a gang in television series Day Break
• Low-definition television (LDTV)

In music:

• Little Doses, a Scottish alternative rock band
• Luis Dubuc

In contracts:

• Liability Damage
• Liquidated Damages, a figure in contract law

LD can also refer to:

• LD, the ISO 3166-2 code for Lakshadweep, India
• LD, the code for Longford, Ireland
• LD postcode area, also known as the Llandrindod Wells postcode area, in Wales
• Learning disability, a condition that can impair learning through standard methods
• Liberian dollar, the currency of Liberia
• Libyan dinar, the currency of Libya
• Liberty dollar, the private currency by norfed
• Licensed Dietician
• Light Dragoons, a British Army cavalry regiment
• Lighting designer, the person in charge of lighting in theatre
• Lincoln–Douglas debate, a form of debate
• Line Drive, a trajectory-related inference and statistic of a batted ball in baseball
• Lilian day, a variant of the Julian day
• Air Hong Kong and Linea Turistica Aerotuy, airlines with IATA code LD
• LD (cigarette), a brand of cigarette from the Gallaher Group
• Living Dangerously, an ECW PPVTemplate:Clarify
• Listening device, used in covert investigations
• Long distance relationships
• Louis-Dreyfus Group, a French commodities trading firm
• Lucid dreaming, a dream in which one is conscious of dreaming as it is happening
• Ludum Dare a rapid game development competition
• Lynsey Dyer, an American freeskier and Big Mountain skier

Ld (Capital L with a lower case "d") is the abbreviated form of:

• Lord, a peer of the realm in the United Kingdom
• Lordi, a hard rock band