CFM (more commonly written as cfm or acfm for average cfm) is a measure of the flow rate of air pushed out by a compressor. It stands for cubic feet (per) minute./
This is important because it directly relates to the suitability of a compressor for a given application.
For example, some tools are continuous-demand appliances and may require a high cfm. Illustrations might include pressure washers or saws.
By contrast, something such as a nail gun might require a very short-sharp burst of air occasionally. There, a lower cfm might be acceptable.
In understanding the suitability of a compressor, it’s typically necessary to consider a combination of operating pressure and cfm in order to be sure that you won’t be disappointed.
As imperial measures give way increasingly to metric in the UK, it might be common to see flow rates measured in litres per minute or some variation thereof.