In my experience, an eBrochure is usually a digital version of a brochure that we have developed for print. This is not always the case, more and more we are designing and creating brochures for our clients with only digital distribution in mind.
The eBrochures that we produce are typically PDF's with varying degrees of interactivity and multimedia included. That interactivity could include as little as linking a table of contents to the corresponding section of the brochure. But they can also include video and interactive items like 3D models and page transitions like page flips.
For most clients, when they request a eBrochure, they just want a digital version of the brochure you're creating, to use on their website or to email to clients. You can use the additional interactivity as an up-sell in most cases and charge more than you would for just a flat PDF copy.