| J | Joule (SI unit) |
| J-CLOT | joint closed-loop operations test |
| J-FACT | joint flight acceptance composite test |
| J-T | Joule-Thompson |
| J-box | junction box |
| J/M | jettison motor |
| J/S | jammer-to-signal ratio |
| JAEIC | Joint Atomic Energy Intelligence Committee |
| JAEL | JSC avionics evolution lab |
| JAN | joint Army-Navy |
| JANNAF | joint Army, Navy, NASA, Air Force |
| JAS | Journal of Aerospace Science |
| JB | junction box |
| JC | job card |
| JCA | jettison controller assembly |
| JCCS | job card control system (subsystem) |
| JCL | job control language |
| JCS | Joint Chiefs of Staff |
| JEA | joint-endeavor agreement |
| JED | julian ephemeris date |
| JEM | EF Japanese Experiment Module Exposed Facility |
| JEM | Japanese experiment module |
| JES | joint environment simulator |
| JETS | joint electronic-type system |
| JFAS | jet fuel accounting system |
| JFET | junction field effect transistor |
| JIC | job instruction card |
| JIP | joint installation plan |
| JIR | job improvement request |
| JIS | joint integration simulation |
| JISWG | Joint Integrated Simulation Working Group |
| JIT | just in time |
| JMTSS | joint multichannel trunking and switching system |
| JO | job order |
| JOA | joint operating agreement |
| JOC | Joint Operations Center |
| JOD | joint occupancy date |
| JOIP | joint operation interface procedure |
| JOIP | joint operations interface plan |
| JOP | Jupiter orbiter probe (Galileo) |
| JOP | joint operating procedure |
| JOR | job order request |
| JOVIAL | Joule's own version international algebraic language |
| JP | jet propellant |
| JP | jet propulsion |
| JPASO | Joint Pacific Area Scheduling Office |
| JPC | joint power conditioner |
| JPIC | Joint Program Integration Committee |
| JPL | Jet Propulsion Laboratory |
| JPO | Joint Program Office |
| JPOC | JSC Payload Operations Center |
| JPP | joint program plan |
| JRB | Joint Review Board |
| JSAT | Joint Structural Assessment Team |
| JSC | Johnson Space Center |
| JSCM | JSC manual |
| JSL | job select logic |
| JSLWG | Joint Spacelab Working Group |
| JST | joint systems test |
| JSTARS | joint surveillance target attack radar system |
| JSTPS | joint strategic targeting planning staff |
| JTA | job task analysis |
| JTG | Joint Training Group |
| JTIDS | joint tactical integrated display system |
| JTIDS | joint technical information distribution system |
| JTS | job training standard |
| JTSC | Joint Test Support Center |
| JURG | Joint Users Requirements Group |