"Abstract" is a board gaming term meant to describe board games that are designed purely for the abstract joy of the game, the theming is light and the rules are as minimal as possible to get out of the way of the interesting strategic implications. What matters is the intriguing mechanics and thus the game appears "abstract" compared to a more heavily themed board game that has lots of rules to help bring to life a particular vision or theme.
Chess, go and backgammon are only some examples of classic abstracts, but there is a vibrant scene of modern board game designers creating similar games.
https://en.m.wikipedia.org/wiki/Abstract_strategy_game
Of course, there is a beautiful continuum, this isn't a binary categorization.
As a side note, one of the board game youtube channels I most highly respect is an australian couple called Thinker Themer where one of them loves board games for Theme and one loves them for Mechanics (someone more like you) and they try to find games that hit all the right boxes for both of them. Even if you are purely a player that plays for mechanics I think it is an interesting perspective on this subject!