Plate solving, which is more formally called Astrometric solving is a technique used to calculate the celestial coordinates (RA and Dec) of any object within an image. As a general rule, the object you’re plate solving for is the target object in the image. The result is that an image capture program like Sequence Generator Pro use this information to make corrections to where your telescope is actually pointing (via your mount) so that in the end, your telescope is pointing at the target you want it to and not elsewhere. It does this by taking an image of the sky where you are pointed to, compare the stars in the image to a reference catalog of the sky and calculates with a high degree of accuracy where the mount is actually pointing versus where it should be pointing. It then calculates the corrections needed to move the mount (and subsequently the telescope) to center on the astrometric coordinates you defined as the target.
Plate solving gets its name from the time of early astrophotography, when camera images were taken on photographic glass plates that were covered with an emulsion to engrave the image to the plate. These photographic plates were then analyzed by teams of women to provide the astrometric solutions to the stars in the plate image. This made it possible to build a complete survey of the sky.
Now, we get the solutions to the question "where in the universe am I pointing?" through the use of computers and sky survey catalogs such as the Gaia catalog to do the work. In the specific case of Sequence Generator Pro, this is done through the use of Pinpoint, PlateSolve 2, ANSVR and other programs containing the different sky catalogs.
With plate solving programs, you may also hear the terms Known-Position solving and Blind Plate Solving. Known-Position plate solving is where you tell the system where you think you’re pointing to and the system will start its search using that starting point as a reference and then confirm how far off you are. This is usually the quickest way to get a solution to know where you actually are and how far off it is from where you want to be. A Blind plate solve is where you do not provide the system any information as to where it might be starting out and it searches blindly for the solution. This process will work well, but you’ll need to be prepared to wait a while longer to get the answer.