Google doesn't have too much information to return search results so it tries to make the most of it. By expanding the query with other related words, Google's search results are more comprehensive. For example, if you search for [photo frame], Google will also find pages that include [photo frames] or mention PhotoFrame, a plug-in for Photoshop.
In some cases, the query expansion removes the original intention of a query. If you replace "blogger" with "blog" in [blogger profile images], the query no longer includes the most important keyword.
To force Google not to change your keyword, add a plus (+) in front of the keyword. Instead of searching for [blogger profile images], you'll use this query: [+blogger profile images]. Alternatively, you could use quotes even for a single keyword: ["blogger" profile images] or add a plus after your keyword: [blogger+ profile images].
If you want to make a query fuzzier, use the synonymous operator (~): a search for [google earth ~images] will include results that contain "imagery", a more appropriate word than "images" for describing Google Earth's satellite pictures.
Depending on your query, Google uses something intermediary between + and ~, by including web pages that contain synonymous or different morphological forms for some of the keywords, but you can explicitly define the importance of your keywords. Use + for the most important keywords that should never be modified or ignored and ~ for general keywords that could be replaced with something more specific.
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