In my opinion this is possibly one of the biggest improvements Google has made to its AdWords product for a long, long time. You can see the official Google launch here.
Prior to this recent launch as a Google AdWords advertiser you had three options in terms of keyword targeting.
This allows your ad to show on search terms Google see's relevant to your keyword. Example, If you had "immigration solicitor" as a keyword, your ad could show for search terms such as "home office".
This allows your ad to show on search terms that contain the exact phrase in your keyword. Example, If you had "football boots" as a keyword, your ad could show for search terms such as "adidas football boots" or "football boots special offers" but would not show for anything that didnt containt your keyword in the phrase.
This allows your ad to show on search terms that contain ONLY the exact keyword in the search phrase. Example, If you had "oakley sunglasses" as your keyword, your ad would only show for that exact search term.
The new keyword targteting match type is:
Modified Broad Match
This allows you to use the advantages of the extended audience reach that broad match brings but with a lot more control. You can add a "+" sign before any of the terms in your keyword and this lets Google know that you only want your ad to appear if the search query includes a particular term or variant (including misspellings). Example, If you had "+garage +flooring tiles" as a modified broad match term then your ad could appear for search phrases such as "garage flooring providers" but would stop your ad from appearing for search phrases such as "kitchen flooring" which it would have done previously under a broad match keyword.
The image below illustrates the reach of different keyword match types. As you can see, modified broad match keywords match more searches than the equivalent phrase match keyword, but fewer searches than the equivalent broad match keyword. Match behavior also depends on the specific words you modify.