In Excel, a spill refers to the behavior of formulas that return a set of values, also known as an array, which are returned to neighboring cells. A #SPILL! error occurs when a formula produces multiple results but cannot output them all on the sheet. This error can be caused by a variety of factors, including:

• Obstructing cells: When the spill range for a spilled array formula isnt blank, the formula will return a #SPILL! error. A dashed border will indicate the intended spill range, and you can select the Error floatie to choose the Select Obstructing Cells option to immediately go to the obstructing cell(s). You can then clear the error by either deleting or moving the obstructing cells entry.

• Invisible characters: In some situations, a spill range may look blank, but in fact, it is not. The problem may be in invisible characters such as a space lurking in some cells, or formulas returning an empty string. To detect such cells, click a warning sign, and you will see this explanation - Spill range isnt blank.

• Dynamic array formulas: Dynamic array formulas can return arrays of variable size, and formulas that are currently returning arrays that are successfully spilling can be referred to as spilled array formulas. However, if Excel cannot determine the size of the spilled array, it will cause a #SPILL! error. For example, sometimes, the formula allows a dynamic collection Excel to change its size between each arithmetic pass. If the size of the dynamic array Excel keeps changing during the calculations and doesnt balance, it will throw a #SPILL! Error.

To fix a #SPILL! error, you can try the following solutions:

• Clear the expected spill range by clicking the formula cell and removing any data inside the spill area or moving the formula to another location where there is no blockage.

• Remove any obstructing cells by selecting the Error floatie and choosing the Select Obstructing Cells option to immediately go to the obstructing cell(s). You can then clear the error by either deleting or moving the obstructing cells entry.

• Refer to a specific range or a single cell instead of a large spill range.

In summary, a spill in Excel refers to the behavior of formulas that return a set of values, and a #SPILL! error occurs when a formula produces multiple results but cannot output them all on the sheet. This error can be caused by obstructing cells, invisible characters, or dynamic array formulas. To fix the error, you can clear the expected spill range, remove any obstructing cells, or refer to a specific range or a single cell instead of a large spill range.