It has also resurrected a host of often confusing geographic terms.

AFP breaks down the two most common -- the ADIZ and the median line.

- ADIZ -

Many nations have so-called air defence identification zones (ADIZ), including the United States, Canada, South Korea, Japan and China.

They are not the same as a country's airspace.

Instead, they encompass a much wider area, in which any foreign aircraft is expected to announce itself to local aviation authorities.

This is intended to allow greater time for a country to identify and respond to potentially hostile aircraft.

Taiwan's ADIZ overlaps with part of China's, and even includes some of the mainland.

Until recently Chinese and Taiwanese military planes largely stayed out of the other side's ADIZ, though occasional incursions did happen.

That began to change about two years ago, as Beijing applied greater military pressure on Taiwan, which it regards as its territory and has vowed to one day take over.

Last year, Taiwan recorded 969 incursions by Chinese warplanes into its ADIZ, according to an AFP database -- more than double the roughly 380 carried out in 2020.

The vast majority of those flights clipped the southwestern corner of Taiwan's ADIZ.

The most aircraft China has sent in a single day is 56, on October 4, 2021.

But the daily drip of incursions is equally important.

Before this week's military drills, Taiwan reported 626 incursions so far this year, an almost 70 percent increase on the same period last year.

The large number of sorties has put Taiwan's air force under immense pressure, and it has suffered a string of fatal accidents in recent years.

- The median line -

The median line is an unofficial but once largely adhered-to border that runs down the middle of the Taiwan Strait, which separates Taiwan and China.

It came about during the Cold War as a way to try and delineate the two opposing sides and reduce the risk of clashes.

No agreement or treaty ever solidified its status. But over the decades it helped keep Taiwan and China's militaries apart.

During times of tension, China would periodically send warships or planes across the line, leading to protests from Taiwan.

But crossings of the median line were generally less common than ADIZ incursions and were seen as more provocative.

Over the last two years, Chinese officials have publicly voiced that in their view the median line does not exist and never has.

There has been a major increase in median line incursions during this week's drills.

Of the 49 aircraft incursions Taiwan reported on Wednesday and Thursday, 44 involved Chinese aircraft crossing the median line.

Taiwan's military on Friday also said Chinese warships had crossed the line but did not give a breakdown.