See above

2. By definition a short film is a feature that is no longer
than 40 minutes including end credits but ideally 10
minutes or less.
A short film may be either professional or amateur
standard as long as it fits within these time constraints.
Other names for a short film are “featurette”, however
this is often coined for slightly longer films that are not
quite feature length, and “short subject”. The latter
name was slowly outmoded as it implies that the film is
not stand alone and is instead a small section of a larger
feature or a subsidiary of a larger feature.

3. By using the definition we can categorise many if not all of the first films as short
films, they were by the most part within the time constraint.
Due to the technology being of a pioneering nature it was extremely expensive
for film makers to make anything longer than a few minutes. As a consequence
films were shown in the cinema as a set. A group of films, not necessarily similar,
that would have been shown at the same time so that movie goers get the best
experience for their money and film makers get
opportunities that were unavailable before.
This is because the only
option for film makers before this were in the
form of Mutoscopes, basically a mechanical
flip books showing cells on rotating spindle.

4. While short films were on the rise many film makers wanted to make films even
longer and the “feature” was born. These were phenomenally popular and forced
short films to take the back seat and be shown along side a feature hence the term
“Short subject” being applied.
However from this other genres were developed as people took more to seeing a
comedy sketch or cartoon reel in between the main features rather than a
traditional short film and so short film sketches were born.
During the silent film era it was common place for many film companies to have a
defined “short film”
department especially during the 1920’s
however as films developed into the “Talkies”
they became more and more rare.

5. Student films… no more need be said. I’m kidding there are entire parts of Indian
cinema dedicated to short films along with animation companies that specialise in
short films and up and coming film companies. It is an easy way for small companies
to make a name for themselves. Whether most of these are student film companies is
neither here no there.
However due to short films being very set in the domain of students there are many
examples some funny, some just sad, of film students making satire or parody or even
more common thrillers, horrors or gritty reality films. The reason for this is because
the are cheap and anyone can do it, the down side is that as definitions develop and
this becomes more common place the meaning of short film, in the future, may be
“student satirical production”… and then the world will end.