Steganography is the practice of concealing something in something else. For instance hiding a text message inside a larger body of text. There is no cryptography. The security of the message, such as it is, is in the form of obscurity. That may be enough. Cryptography is computational expensive and required management of encryption keys. And it is no more secure that the keys employed. It appears that the better cryptographic algorithms are quite good and attacks tend to focus on the keys.
Attacking steganography would be different. Rather than asking Where is the key, one would ask is there anything there at all ?
There are applications for conducting steganography. Capable of embedding a message inside an image for example. But this is not about conducting steganography.

What I am after here is for application itself to be steganographic. To conceal the application, not inside another application, like a trojan, but altogether.

What would it mean for an application itself to steganographic.

Imagine an application as a book. And using an application as equivalent of reading a book from cover to cover.
Lets further imagine that we cut the the spine of a number of books and shuffle the loose pages together like so many decks of cards. Assuming uniformity of paper quality and page size, layout and font, and no metadata on page – having a loose page tells you little about which book it was from. Or if it came from any book at all.
If you have access to the full text of the original books that were shuffled together, you could do a text comparison and quickly identify which book the page came from. But in the absence of that there would be little to go on. Analyzing the text on the pages would yield some clues and more or less probable guesses could be made. Particularly if the books had comparatively few pages, i.e. if any one page contained a large fraction of the complete text.
The obfuscation could be further improved by cutting the pages up into individual lines of text.
Identifying a line as belonging to only one particular book would be difficult in many cases.

On a side note: what difference does it make cutting the pages up along the lines or across them, for the purposes of putting back together the original page. Again assuming uniformity of paper, layout and font. I venture that a line of text is harder to mach than a column of text. There is a certain balance here. While a line contains more meaningful information, a whole sentence perhaps – it also has fewer markers, fragments of words, that would match it to the strips of paper on either side of it. You gain information in one way and lose it in another. Specifically the anchoring within the larger body.

But the analogy we’re pursuing here is application functionality as reading a complete text: whole book to page to line.

Alright, so we have a large pile of individual strips of paper. Now, how do we read the book?

The premise being that the application, the book in out analogy, is concealed among a large body of code. Where only those knowing exactly what to look for, can find it. The secret in steganography is not the decryption key but how to find what you are looking for – the detection key if you will.
A steganographic application would have to have a detection key. With which you can locate the application and without which you can not. A link to first page, in the book analogy.

In a book you can just turn the pages but here all the pages are separated from one another. How do you get from page to page – or from one line to the next, in the more fine grained analogy.

Each page has a link to the next page but that link is only usable to someone who has a key. Else anyone stumbling on a page would discover the whole book. The idea was that a page does not guarantee a book. Given a pile of pages you can’t know how many books are in it or even if there are any at all. All you have are disjointed pages. Or code.