Google’s Plus Operator, No Longer Available
The plus operator from Google Search was useful to highlight one or more keywords that had to be included in the search results exactly as you typed them. If you search for [ai], Google matches terms like “artificial intelligence”, “Amnesty International”, “Art Institutes”, “Appraisal Institute”, “Adobe Illustrator” and that’s not so useful. To restrict the results to pages that include “ai”, you had to replace your query with [+ai]. Unfortunately, the plus operator is no longer available and you now have to use quotation marks even for single words and search for [“ai”].
“Google employs synonyms automatically, so that it finds pages that mention, for example, childcare for the query [ child care ] (with a space), or California history for the query [ ca history ]. But sometimes Google helps out a little too much and gives you a synonym when you don’t really want it. By putting double quotes around a single word, you are telling Google to match that word precisely as you typed it,” informs the Web Search help center.
The plus operator was easier to use for single words and it was intuitive, considering that the minus operator is employed to exclude results that contain a certain word. Maybe Google wants to use the operator to integrate Web Search with Google+.
By Google Operation System. Read the announcement here.