Like any long-running sci-fi series, Doctor Who has given us a lot of great technobabble over the years. Some of these sayings have a specific purpose - for example, "dimensionally transcendental" is just a great way of saying that something is bigger on the inside than the outside. Others can apply to, well, basically anything at all, as is the case with "reverse the polarity of the neutron flow".
One of my favorite examples of technobabble belongs in the former category. It's first mentioned in "Day of the Daleks", featuring the Third Doctor and Jo Grant. The story features a group of fanatics from a future where Earth is ruled by the Daleks. The event that led to this future was the bombing of a world peace conference, led by Sir Reginald Styles. Because they believe that Styles is responsible, they try to assassinate him multiple times.
At one point, Jo asks the Doctor why the guerillas can't simply go back in time to when they first tried to assassinate him and get it right this time. The Doctor says they can't because of "The Blinovitch Limitation Effect". He doesn't expand on this, at least not in this story. But even here, it's a great little piece of technobabble. The context at least addresses a key question of time travel stories: namely, why can't you go back in time to the exact same point more than once?
It's a simple question, but also one worth asking. Initially, it's no real explanation, just a simple rule to prevent time travel in Doctor Who from becoming too complicated. But over time, it's a rule that's been expanded on and became rather crucial.
Energy
The Fifth Doctor story "Mawdryn Undead" expanded greatly on what the "Blinovitch Limitation Effect" actually was. Simply put, if someone meets their past/future self, the paradox resulting from such a meeting could unleash an incredible amount of energy.
This very effect happened in the Fifth Doctor story "Mawdryn Undead" when two versions of the Brigadier - one from 1977, the other from 1983 - touched each other. The energy released from this would normally be incredibly destructive, but thankfully, the energy was unleashed at exactly the right moment and absorbed elsewhere.
Interestingly, this doesn't seem to affect Time Lords, at least not those meeting their earlier/later selves. In all of the multi-Doctor stories on television - and even the only multi-Master story - we've never seen sparks fly. (Well, not literally.) However, when the sonic screwdriver came close to touching its slightly older counterpart in "The Big Bang", a spark was clearly seen. It might be that Time Lords aren't quite as affected by the effect due to a property of regeneration. But there is another effect that happens when different incarnations meet each other.
Amnesia
Another symptom of the Blinovitch Limitation Effect is amnesia, which makes sense. After all, in all multi-Doctor stories, despite essentially living exactly the same event multiple times, the later Doctors have no memory of the adventure. Again, while the effect isn't named in these stories, it is a nice way of avoiding making the time travel element of the show too complicated.
In the multi-Doctor stories from the Classic Series - such as "The Three Doctors" or "The Five Doctors" - the amnesia effect is only implied, at best. But in the multi-Doctor/multi-Master stories written by Steven Moffat, the effect is more explicit. And there are hints that later incarnations remember something, at least, even if the memory isn't a clear one.
For example, in "The Day of the Doctor", when the Eleventh Doctor sees a time fissure suddenly open, he says that he "almost remembers" it, to the point that he knows it's the exact moment his previous self meets him.
Out of sync
At the end of the 50th anniversary special, the amnesia is addressed even more directly. When the War Doctor realizes that he won't remember saving Gallifrey, the explanation is that "the timelines are out of sync". While Blinovitch isn't named directly, the idea of earlier Doctors forgetting such encounters does seem to fit as a side effect.
The Blinovitch Limitation Effect is such a great piece of technobabble because it has a clear function: keep time travel simple. Yes, you can have Doctors and even companions meeting their older/younger selves, but you need to establish clear rules to avoid the story becoming too complicated. In its first vague reference in "Day of the Daleks", the effect nicely handwaved why you can't - or at least shouldn't - go back to the same point in time twice.
The best pieces of technobabble have a clear reason for why they're stated. The Blinovitch Limitation Effect is a perfect example of that.