The difference between a pre-strung and unstrung tennis racket is that a pre-strung racket comes with strings already installed, while an unstrung racket does not have any strings installed and must be strung before use.
Pre-strung rackets are convenient for players who are just starting out or who don't want to go through the process of selecting and installing their own strings. They typically come with basic strings that are suitable for a wide range of players, but can be upgraded with higher-quality strings for more advanced play.
Unstrung rackets are preferred by more experienced players who want to select their own strings to match their playing style and preferences. They can choose from a variety of strings with different materials, gauges, and tensions to customize their racket's performance.
It's worth noting that some manufacturers offer both pre-strung and unstrung versions of the same racket model, allowing players to choose the option that best suits their needs.