The VLOOKUP function is a built-in Excel function that helps you look for a specified value by searching for it vertically across the sheet. It is used to find data in a table or a range by row. In its simplest form, the VLOOKUP function takes four arguments: the value you want to look up, the range of cells in which the VLOOKUP will search for the lookup value and the return value, the column number in the range containing the value to return, and whether to return an approximate or exact match. The function searches for a certain value in a column (the so-called table array), in order to return a value from a different column in the same row. VLOOKUP is commonly used for data retrieval and analysis tasks.