A slicer is a tool used in data visualization software, such as Microsoft Power BI or Tableau, that allows users to filter data interactively. It provides a user-friendly way to narrow down data sets by selecting specific criteria, such as dates, categories, or numerical ranges. This helps users focus on relevant information without altering the underlying data. Slicers can be displayed as buttons, dropdowns, or sliders, making it easy for users to manipulate the data view. They enhance dashboards and reports by allowing for dynamic exploration of data, leading to better insights and decision-making based on the filtered results.