The term used to describe the expenses incurred when purchasing or selling a financial instrument is known as the "transaction cost". This includes any fees or commissions charged by brokers or other intermediaries involved in the transaction.
The transaction cost can have a significant impact on the overall profitability of a trade, especially when dealing with smaller profit margins or shorter timeframes. As such, it is important for traders to carefully consider and compare transaction costs across different brokers and trading platforms before making a trade.