What modified broad match was
Modified broad match was a keyword setting marked with plus signs in front of individual words. A keyword written that way told Google that every marked word, or a close variant of it, had to appear somewhere in the search, in any order, with other words allowed around them. It sat between phrase match and broad match: wider than a quoted keyword, far more disciplined than plain broad.
It no longer exists as a separate type. Google folded its behaviour into phrase match, stopped accepting new modified broad keywords, and left the old ones running. Any keyword still carrying plus signs is treated as a phrase match keyword, and the plus signs themselves do nothing. Nothing breaks, which is precisely why so few people notice.
Why it still matters
Because the syntax survives everywhere except in the product. Keyword templates, training decks, agency proposals, spreadsheets handed between staff and a great many blog posts still describe the plus-sign method as a live technique. In Nepal I regularly see it in inherited accounts and in proposals written by people working from older material.
That matters for two reasons. A structure built on a control that has been switched off is not the structure the writer thinks it is, and a report comparing today’s results against a period when this type genuinely behaved differently is not comparing like with like. Both quietly mislead.
Where it goes wrong
The most common error is trust. Someone pastes an old keyword list, sees the plus signs sitting there in the interface, and assumes the words are being enforced. They are not, so searches arrive that the plus signs were supposed to prevent, and nobody investigates because the setup looks correct on screen.
The second is in proposals. If a document you are being asked to sign promises a modified broad match structure as part of the method, that is a fair sign the approach has not been reviewed for some time. It is a useful, polite question to put to any prospective agency.
The third is misreading history. Performance from the period before the change reflects a matching rule that no longer applies, so it makes a poor baseline for judging a current campaign.
What to do about it
In a live account, leave the keywords running if they are performing — they are ordinary phrase keywords now — but strip the plus signs the next time you rebuild the list, so nobody inherits the confusion. Then get the control you actually wanted from the two places it now lives: choosing the right keyword match type for how confident you are about a term, and maintaining negative keywords from the search terms report.
If you have taken over an account that was built around this method, treat the whole keyword structure as a candidate for review rather than as a working design. Check what the search terms report shows now, not what the naming convention implies, and rebuild from that evidence.