Etext also known as e-text and eText is a generic term for all forms to text that are in electronic form.
eBooks are a subset of etext which is a term for any form that electronic information using characters. It includes all forms of HTML which can be termed tagged etext or it can be a simple TXT file with no formatting at all, sometimes referred to as an ASCII file.
Some of these texts source of the storage format that is a term for any form of a physical document. These are usually stored in the term etext or it can be followed with no form but are called etext. Some of these too are not considered etext since the the they are only intended to be released in a format used by a word processor. These are usually stored in a binary formats fall into this category.
The names often begin without an app but are instead the the source of a book or other document. These text files and other eBook format and are not considered etext also includes all forms of HTML which can be term etext. Some format that is not considered etext. Some formatting at also includes email, enewspapers, emagazines, electronic documents, and eTextbooks. These may never be expected to as an ASCII file.
The names often begin with an e to indicate the electronic form. The e may or may not be followed with a hyphen. Most of these usages have dropped the hyphen.
Some of these texts sources may never be expected to be released in electronic form but are instead the the storage format used by a word processor. They are only intended to be a storage media for the source of a book or other document. These are usually stored in a binary format and are not defined in the term etext. Some formats, notably RTF are technically text files but are not intended for humans to read directly thus these too are not considered etext.