FD

FD or similar may refer to:

Medical

• Familial dysautonomia or Riley-Day syndrome, a nervous system disorder

Science and technology

• Canon FD lens mount
• Fermi–Dirac statistics
• Ferredoxin, a molecule functioning in electron transfer
• File descriptor, a component in the Unix operating system
• FreeDOS, an open-source DOS-compatible operating system
• Functional dependency, a constraint in a relation from a database

Transportation

• Thai AirAsia's IATA code
• FD (Mazda RX-7), model designation for third generation Mazda RX-7
• FD Phantom, original name for the FH Phantom jet fighter
• Steam locomotive FD, a Soviet steam locomotive
• Flight director (aviation)
• Class symbol for the Flying Dutchman (dinghy) class

Other uses

• Fidei defensor (latin), a subsidiary title used by British monarchs
• Fixed deposit, a financial instrument provided in India
• Finance Director, manages a company's financial affairs (used chiefly in the UK)