I never know what it means either. But, as I understand it, the Starmeter rating is given to everyone who is entered on the system (this probably includes the writers, directors, and crew listed as well - I'm never quite sure - but, as actors, we tend to forget the fact that IMDb is by no means only a directory resource for actors' listings - its a directory for everyone involved in the world of movies).
The ranking is given initially on the basis of decisions so arcane I have never yet been able to work them out - I *think* your rating is decided on the basis of things like how highly rated the projects you have featured in are riding within the general consensus of the industry, what sort of ranking your co stars in a film are obtaining (and, let's be honest, it may be the case that you shared the screen with Tom Cruise or it may be the case that you were one of 3,000 extras standing in a street scene in a film Tom Cruise was in - both will be acceptable on IMDb if you were credited - calling other actors your 'co stars' is, therefore, a relative term!), and so on - but no-one I have ever asked appears to know for certain.
What can be said is that IMDb - as I never get tired of mentioning- started as a fan site, so there is meant to be a correlation between the Starmeter ranking and how 'hot' a property you are considered to be in terms of...whatever indices IMDb is using to decide that. Some maintain that things as simple as the number of hits you get from internet searches run on you increase your rating - because this shows you are of more interest to the public at large, and this may well be true - but I don't think it's the only reason ratings go up.
By and large, if there is an upsurge of interest in a project you have been listed as appearing in, an upsurge of interest in someone who you have appeared 'alongside' because of another project, an upsurge in the number of hits your profile is receiving, an upsurge in interest in the general genre of one of the films you have taken part in, an upsurge in interest in the work of a writer whose words you have performed, sales of one of your projects to a new distributor, or, frankly, I don't know what, then I *think* your rating goes up. And when that surges dies down, then it tends to fall as rapidly.
Equally, it's my understanding that everyone (as I say) is listed on the Starmeter when they are first flagged on the system - so shifts in the system are calibtrated, somehow, against all other shifts in the system. Therefore, I'm also of the opinion that *you* don't have to achieved anything personally for your rating to go up - it's enough for the person just ahead of you in the ranking to have a very bad week, fall precipitously from a higher ranking position, and your rating will rise in response because everything is relational to everything else.
I know that on IMDb Pro you can call up the graphs of all this, but even then, I wouldn't say you learn vast amounts about what's *actually* going on.
When all this is summed up, it sounds so *insanely* complicated that I have no idea how IMDb actually regulates the ratings, and perhaps it is much simpler than even I have been assuming: something like you are entered at a very basic entry level rating, and then the database can calibrate the relative popularity of films and other actors you have worked with and offsets these against your rating. I assume someone who is doing extremely prevalent work rises very quickly. I don't imagine they have a round the clock team of researchers whose every waking hour is devoted to discovering what's 'hot' and what's 'not' for every film on their database. I mean, they are supposed to list everything ever filmed for broadcast in the last hundred odd years aren't they? They cover both films *and* TV. They're an international database, and they have thousands and thousands of people logged on the system, so it cannot be calibrated except in regard to some very broad categories.
True, computers are able to do amazing things with analysing and graphing algorithms that ordinary human beings couldn't conceive of doing in a similar amount of time (or, indeed, ever) - and that must be part of it...but truly, who knows? I am waiting for someone to enlighten me!