h-entry (which, along with h-feed is the microformats2 update of the former hAtom) is a draft standard intended to be one of several "microformats" released via the microformats.org site and community, intended for the representation of information in a manner that is human-readable but can still be processed by machines.
The format encodes a subset of the Atom feed standard in the form of a standardized set of elements, attributes, and classes in HTML or XML. Thus, it can be embedded in web pages and be readable this way (and styled via CSS), but has a standardized structure that can easily be converted mechanically to other formats as needed for machine processing.
It is intended particularly to encode a blog entry (or other item that is datestamped and intended to be part of a series) to provide metadata which might be useful in generating feeds. The h-feed format contains a series of such entries.