What is zoom?
The term can have multiple meanings. In our context, it describes magnifying or shrinking a portion of a page. Wikipedia puts it this way:
In computing, page zooming is the ability to zoom in and out a document or image at page level. It is usually found in applications related to document layout and publishing, e.g. word processing and spreadsheet programs, but it can also be found in web browsers as it improves accessibility for people with visual impairment and people using mobile devices, such as PDAs and mobiles which have a relatively small screen.
On Android, in most applications supporting "zoom" it is triggered either by double-tapping, or the so-called pinch-to-zoom, where two fingers are used to pinch or spread the viewed object/area.