State estimation refers to the process of determining the current state of a system based on measurements and a model of the system dynamics.
States can be anything, it doesn’t have to be a position. Ex: In the context of aircrafts, you can do state estimation for the fuel level and engine performance.
Seen from Visual SLAM book:
Whether the motion and observation equations are linear and whether the noise is assumed to be Gaussian, it is divided into
- linear/nonlinear and
- Gaussian/non-Gaussian systems