The unbroken line (連綿) is a very characteristic element to both Chinese and Japanese calligraphy art. It is easily detectable in cursive script (草書), perhaps even more defined in Japanese kana script (かな). The unbroken line technique is also applied in semi-cursive script (行書), and even some styles of standard script (楷書).
The concept of the unbroken line is based on either direct or indirect (visible or invisible) connection between the strokes within one character, or between two or more characters.
If you look at the above picture, you will notice that both halves of the right-hand side character 雖 (although) are connected with one brush stroke. Although, in the left-hand side character both halves are separated, the connection is invisible. The brush leaves the paper surface and traces a curved line in the air, to the point where it descends onto the paper once more, in order to complete the right half of the Chinese character.
The unbroken line (especially the invisible one), aside defining / altering the structure of Chinese characters executed in a given script, it introduces a rhythm of writing. That rhythm is the foundation of writing Chinese and Japanese calligraphy (especially in "faster" scripts).
To be able to apply the unbroken line technique, one has to master the stroke order of Chinese character, and rules of writing in a chosen calligraphy script. This technique does not allow for hesitant writing.
I intentionally placed the unbroken line tutorials in the section referring to cursive script, because this technique is mostly used during writing in running hand.
Ponte Ryuurui (品天龍涙)