...
Here you can define the particles' initial speed. Higher values will generate more particles per frame and faster particles act with stronger forces on other particles or objects. The number of emitted particles also depends on your “Resolution” settings. A value of 0.0 disables the emission of particles. This value can be animated either with keyframes or expressions. "Speed" is measured in metres per second [m/s].
V/H random
By default the particles are regularly emitted, showing a kind of pattern. The reason is that the particles are emitted as a homogeneous stream. To avoid and suppress this pattern, it is possible to randomly displace the particles with these functions. The values should range between 0 and 1, but can be higher, as well. “V” stands for vertical, while “H” means horizontal.
...