Retrograde. Basically when a
planet seems to move in
reverse. Each planet
rules over different set
aspects of life, almost
strengthening and protecting them. However, when the planet turns away from it's usual schedule,
orbit, it also works against what it's
purpose is.
Mercury is the planet of communication, be it business, familial, or just plain interpersonal. It speeds along, smoothing over the bumps and pitfalls life throws at us. 'You can talk anything out'. The messenger in every way. But when this planet runs backwards, communications are down. It isn't unlikely for your 'puter to crash, your office to be in upheaval, your girlfriend to say, "we never talk anymore", and your mom to call you saying, "you never call me!", all in the first few days of Mercury in retrograde.
And this occurs a few times each year! How frustrating is that? You may be misunderstood, you may become tactless where normally you are silver-tongued, you may feel as if no one can relate to you. But speak your piece anyway, as to not at least try and communicate leads to it's own problems.