Why google added some words in Search result title

[Amyjackson92]

I have added meta titles in several pages of my website. when i check my site in google search engine, it shows my site's search results with my meta title and also added a keyword in meta title in all my subpages.

For example:
Suppose my domain is : widget-direct.etc
And my Subpage meta title is : "Widget Theory Test Practice 2017"
then why google added some words in google search titles?
Search Result shows the title is: "Widget Theory Test Practice 2017 - Example Test"

i did not understanding, why google adding this word "Example Test" in my all subpages titles in search results, whereas this word is not in my Meta titles.

[edited by: not2easy at 10:10 pm (utc) on Mar 28, 2017]
[edit reason] Anonymizing [/edit]

[phranque]

did you use those words in the search query?
do those words appear in (on site or inbound) anchor text linking to that URL?
do those words appear on that page in the vicinity of the text used in the title?

[Robert Charlton]

In renaming titles, Google likes to add the brand or site name name when it can, along with a summary query phrase. The idea is that the query phrase gets highlighted and draws the eye... the brand name suggests whose site it is... and the combination effectively promotes click-throughs.

Google would probably derive this brand name not just from the domain name alone, but also from inbound links and text on the site. The query phrase is generally included for relevance. The length of the title is also a factor. (The original post has been exemplified enough that I'm not sure what the original situation was).

For a discussion on commonly observed patterns which have more or less been the default for a while now, see this thread. Some members like the rewrites; some don't.

Google is now rewriting all my page titles
Aug 2012
https://www.webmasterworld.com/google/4480232.htm [webmasterworld.com]

Note that the default title length has changed with different Google serp layouts, but otherwise this pattern has remained fairly constant...

Summary Query Phrase - BrandA Widgets

[edited by: not2easy at 2:23 pm (utc) on Mar 30, 2017]