What you [the original post] describe is usually referred to as crouch jumping.

As a marine, you can make a second jump if upon landing your downward vertical speed is less than your maximum run speed. Practically this means you want to minimize the time spent falling after a jump.

This can be done by bunnyhopping up map architecture, or by making the first jump from a crouch.

To crouch jump, you want to start ducking some time before the first jump so that you make the jump just as you finish ducking. It takes some practice to be able to do this consistently. If you jump too early you will jump from a stand; if you wait too long the crouch will take away your speed.

This is usually done in conjunction with what is often referred to as glide jumping, which I will describe below.

Glide jumping is more or less a strafe jump - I believe it takes angular momentum from spinning and converts into regular momentum.

That's somewhat misleading, at least semantically. There is no notion of rotational inertial in NS, let alone of angular momentum.

The speed boost derives purely from translational motion. In general, whenever your horizontal path traces out a curve, you will gain speed. I have seen several explanations for this, but unfortunately none that have fully accounted for every instance of this effect, so I can only resort to a specific description for each case.

The glide jump, at least as I have seen the term used, refers to the use of this effect on the ground by gradually rotating the view while running in some direction in order to increase speed, and then jumping to avoid losing this speed boost to friction. Usually the running direction is 45 degrees displaced from the direction of aim (accomplished by holding forward and a strafe key) with the view rotated in the same direction, for this will result in motion in the direction of aim.

Use of this effect in the air, on the other hand, requires a directional movement command perpendicular to the direction of motion accompanied by gradual view rotation (in the general case), and is commonly referred to as strafeturning. Usually this means holding a strafe key (only) and rotating the view gradually in the same direction, for this will result in forward motion. This increases your speed and will also gradually change your direction of motion so that it remains aligned perpendicularly to the directional command (that is, aligned with the direction of aim in the usual case). If the directional command is displaced less than 90 degrees from the direction of motion, it will have no (significant) effect; if it is displaced too far past 90 degrees, it will start to slow you instead.