You'd first have to start with the definition of Frame Rate.
By definition, it's the frequency of frames per second (Wikipedia).
By default, your computer/iOS/Android device performs all actions at a "normal" speed; a "normal" frame rate.
When people say "frame rate hack", they're referring to a third-party client that alters the frame rate usually by a dot-decimal percentage.
Some applications have the ability to alter it within a single program/app, but most just alter everything on the device; whether it's a computer, iOS, or Android.
They usually have the ability to both increase and decrease the frame rate, altering the run-time respectively.
More often than not, people in the gaming realm seek to increase the frame rate rather than decrease, because there's very few circumstances where it would be beneficial to slow down your game.
Increasing frame rate on a game such as Era means that everything processes faster.
Since the whole client is being processed faster, it doesn't discriminate on what is enhanced.
Everything in the client is processed at an equally accelerated rate: walk speed, all bullet speed, reload speed, fire rate, freeze, vehicles, the 'Start' bomb in a spar, Halloween lights,
everything. This includes all animations, scripts, etc.
Please note, that other people don't see any increase in bullet speed, nor spar-bomb speed, etc.
And all animations look normal to others.
It's just pretty obvious when somebody is moving quicker, reloading quicker, shooting more bullets than normal, and getting a head start in spars.
This server isn't as educated on these things as the PC servers, but everybody knows when something looks fishy.
They've been around for years-- I remember the first big one on PC Era back in 2005.
Over the years, Era has developed a pretty effective system to catch these.
It constantly monitors frame rate, and echos RC when it's over a certain percentage faster or slower.
In the past, a PR would then stealth themselves and warp to the individual in question, and be an eye-witness to their debauchery.
Lately, it's been made very easy on PRs; they only have to run a speedhack test on RC.
The speedhack test runs a behind-the-scenes timer of about 15 seconds on your account then determines how many seconds have gone by for you.
If, during those 15 seconds, your client has had increased framerate, your test would return with a result of,
"In 15 seconds, 23 seconds have lapsed".
Then would echo: "Yes! They are speedhacking." on the RC.
The PR would then jail you for speedhacking, and use the above result as evidence.
Recently though, PR intervention isn't even necessary.
The NPCServer has been scripted to perform these tasks by itself.
This is what happens when people are "jailed for frame rate hacking".
Cited Source:
http://en.wikipedia.org/wiki/Frame_rate