Engineers create the organization's products. They are the technology or discipline specialists, the designers, and the gurus in those products.
Engineers maintain a locus of expertise in a specific engineering discipline, technology, or professional specialty. They use their expertise to design, build, and install "solutions." A solution may be a physical asset, software, or a design of intellectual property. They may create it from scratch, or procure vendors' products and then add value.
They also enhance, tune, repair, configure, and support those solutions. This definition does not distinguish those who design and build products from those who repair them. Essentially the same professional specialty is required to do both. Engineers sell anything that requires in-depth expertise in the design of the organization's products -- knowledge of what's inside that black box.
In many functions and industries, there are multiple layers of Engineers. Some design fully assembled products; others are experts in components that go into various products.
Those who assemble components into complete products (the top layer) are called "Applications Engineers." They produce purpose-specific products.
All lower layers are termed "Base Engineers." They design the components that go into various applications. These components are purpose-independent.
For example, civil engineers are Applications Engineers; they build bridges. They employ a wide variety of Base Engineers, such as stress engineers, electrical engineers, and traffic engineers, who contribute parts and advice.
Architects (Applications Engineers, in this framework) who build buildings employ the same list of Base Engineers.
In a corporate example, Applications Engineers design the company's ultimate products, like cars and trucks. They employ Base Engineers who design engines, suspensions, interiors, manufacturing processes, etc.
In IT, the term "application" refers to data-object-specific software -- systems designed to handle information about a particular topic. Base Engineers sell and support computing, database, and telecommunications platforms; end-user computing tools; software-engineering tools and methods; and information-handling disciplines such as artificial intelligence.
In any industry, the domains of Engineers are defined in terms of a specific domain of technology, field of science, professional discipline, or branch of engineering.