Final answer:
In the expression {{ 'sections.slideshow.previous_slide' }}, 'sections' refers to a string key within an object, typically used in a web templating engine to reference a segment of an associative array or nested data structure.
Step-by-step explanation:
In the provided expression {{ 'sections.slideshow.previous_slide' }}, the term 'sections' refers to an object key within a template language. In context, the syntax resembles that of a templating engine used in web development, such as Handlebars, Liquid, or Twig. These engines provide a way to separate the logic from the markup, which allows developers to insert or manipulate content on a web page. The {{ ... }} syntax is typically used to output the contents of a variable or the result of an expression.
In this case, 'sections' is part of a path or a key in an associative array or object, which is used to access nested data. It is not a function (b), a variable in the usual sense (a), nor a conventional array (c). Rather, it denotes a segment within a larger data structure that is being accessed. So, the correct answer to what 'sections' refers to in the given expression is d) a string, considering that it is part of the string key used to retrieve a specific value.