The "exact match" reference means that you need to change the "Match Types" in the left-hand column to exact only (untick "broad", tick "exact")
That will show how many people searched for that precise expression on Google.
So for example, if you enter "car navigation" and click "exact match" you'll see how many people searched for "car navigation" last month, but the number won't include "car navigation system", "car satellite navigation", "gps system" or whatever else Google broad matches to the term "car navigation".
It's this tendancy by Google to conflate so many terms (even ones that don't contain ANY of the keywords) into broad match that makes the choice of exact vs broad so very important, as the latter tells you next to nothing!
Note that you'll probably want to go into the "Advanced Options and Filters" section and choose "Locations: United Kingdom" and "Languages: English" for the most precise possible estimate of how many folks in the UK are searching for that specific term (which is THE most relevant stat if you're talking about a .co.uk domain that matches that search term)