The spread describes the difference between the bid price and the ask price. This is also referred to as the "bid/ask spread“. You sell at the bid price and buy at the ask price.
The spread is usually variable and is different for each financial instrument. Some securities have a low spread, while others have a very high spread. Low spreads are observed, in particular, when a security is highly liquid, in other words there are many market participants willing to buy or sell. When securities are less liquid or in market phases where fewer market participants are willing to trade, the spread is often somewhat higher.
The market determines the price and, therefore, the level of the spread. Trade Republic has no influence on this.