Which of the following refers to applications that may combine data from several business systems across the web?

The correct answer is mashups. A mashup refers to a web application that integrates data and functionalities from multiple sources, often drawing from several business systems and APIs available online. This allows users to create a composite application that leverages these diverse data streams to provide enhanced functionality or new services.

For example, a mashup could combine data from a financial database, a social media platform, and a mapping service to provide a comprehensive dashboard for financial analysts, enabling them to view geographic trends in financial data.

The other terms, while related to applications in some contexts, do not specifically denote the integration of multiple data sources like mashups do. Vertical-market applications typically refer to software tailored for a specific industry. Web applications are broad and simply indicate applications accessed via a web browser, and customized applications are developed to meet specific user requirements but do not inherently imply the combination of various systems or data sources.