- associative memory
- associative multiplication algebra of a nonassociative algebra
- associative ring
- associator
- assort theorem
- assumed elevation
- assumption of plane cross-section
- assumption of straight line
- A-stability
- A-stability of implicit Runge-Kutta methods
- asteroid
- asteroidal belt
- asteroid or minor planet
- astrodynamics
- astrofix measurement
- astro-geodesy
- astro-geodetic deflection of the vertical
- astro-geodetic network
- astrogeodynamics
- astrograph
- astro-gravimetric leveling
- astrolabe
- astrometry
- astronautic remote sensing
- astronomical azimuth